• Korean Journal of Materials Research
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• v.8 no.4
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• pp.328-336
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• 1998

In metal-carbon system with no mutual solubility between matrix and alloying elements as solid or liquid phases, Cu-C-X nanocomposite metal powders were prepared by high energy ball milling for solid-lubricating bronze bearings. Elemental powder mixtures of Cu-lOwt.%C- 5wt. %Fe and Cu- lOwt. %C- 5wt. %Al were mechanically alloyed with an attritor in an argon atmosphere, and then microstructural evolution of the Cu-C-X nanocomposite metal powders was examined. It has been found that after 10 hours of MA, the approximately 10$\mu\textrm{m}$ sized Cu-C- X nanocomposite metal powders can be produced in both compositions. Morphological characteristics and microstructural evolution of the Cu-C-X powders have shown a similar MA procedure compared to those of metal-metal system. As a result of X - ray diffraction analysis, diffraction peaks of Cu and C were broaden and peak intensities were decreased as a function of MA time. Especially, the gradual disappearance of C peaks in the X- ray spectra is proved to be due to the lower atomic scattering factor of C. The calculated Cu crystallite sizes in Cu- C- X nanocomposite metal powders by Williamson- Hall equation were about lOnm size, on the other hand, the observed ones by TEM were in the range of 10 to 30nm.

• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1245-1251
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• 1999

Phase-change optical disk very rapid recording, high densification of data, resulting in high feedback rate and good C/N(carrier to noise) ratio of a feedback signal. However, repetitive thermal energy may cause the deformation of a disk or the lowering of an eliminability and a cyclability of the recording. The lowering of the cyclability can be reduced by insertion of thin layer of ZnS-$SiO_2$ dielectric thin film in appropriate disk structure between the upper and lower part of the recording film. Using the Taguchi method, optimum conditions satisfying both the optimized quality characteristic values and the scattering values for film formation were found to be the target R.F. power of 200W, the substrate R.F. power of 20W, the Ar pressure of 6mTorr, and the electrode distance of 6cm. From the refractive index data, the existence of the strong interaction between the electrode distance and Ar pressure was confirmed, and so was the large effect of the electrode distance on transmittance. According to the analysis of TEM and XRD, the closer the electrode distance was, the finer was the grain size due to the high deposition rate. However, the closer electrode distance brought the negative effect on the morphology of the film and caused the reduction of transmittance. AFM and SEM analyses showed that the closer the electrode distance was, the worse was the morphology due to the high rate of the deposition. Under optimum condition, the deposited thin film showed a good morphology and dense microstructure with less defects.

• Korean Journal of Remote Sensing
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• v.24 no.6
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• pp.559-569
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• 2008

The Geostationary Ocean Color Imager (GOCI) on board the Communication Ocean Meteorological Satellite (COMS), the first geostationary ocean color sensor, requires accurate atmospheric correction since its eight bands are also affected by atmospheric constituents such as gases, molecules and atmospheric aerosols. Unlike gases and molecules in the atmosphere, aerosols can interact with sunlight by complex scattering and absorption properties. For the purpose of qualified ocean remote sensing, understanding of aerosol-radiation interactions is needed. In this study, we show micro-physical and optical properties of aerosols using the Optical Property of Aerosol and Cloud (OPAC) aerosol models. Aerosol optical properties, then, were used to analysis the relationship between theoretical satellite measured radiation from radiative transfer calculations and aerosol optical thickness (AOT) under various environments (aerosol type and loadings). It is found that the choice of aerosol type makes little different in AOT retrieval for AOT<0.2. Otherwise AOT differences between true and retrieved increase as AOT increases. Furthermore, the differences between the AOT and angstrom exponent from standard algorithms and this study, and the comparison with ground based sunphotometer observations are investigated. Over the northeast Asian region, these comparisons suggest that spatially averaged mean AOT retrieved from this study is much better than from standard ocean color algorithm. Finally, these results will be useful for aerosol retrieval or atmospheric correction of COMS/GOCI data processing.

• Journal of the Korean Magnetics Society
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• v.8 no.6
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• pp.335-340
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• 1998

Colossal magnetoresistance $La_{0.67}Ca_{0.33}Mn_{0.99}^{57}Fe_{0.01}O_3$ material has been produced by a metal-salt routed sol-gel process method. Magnetic properties of $La_{0.67}Ca_{0.33}Mn_{0.99}^{57}Fe_{0.01}O_3$ have been studied with x-ray diffraction, Rutherford back-scattering spectroscopy(RBS), vibrating sample magnetometer, and Mossbauer spectroscopy. Crystalline $La_{0.67}Ca_{0.33}Mn_{0.99}^{57}Fe_{0.01}O_3$ was perovskite cubic structure with a lattice parameter $a_0=3.868$\AA$$. And there was no appreciable change in the value of the lattice parameter when a small amount (x=0.01) of iron was added. However, Mossbauer and VSM data indicate the Curie temperature of the $La_{0.67}Ca_{0.33}Mn_{0.99}^{57}Fe_{0.01}O_3$ decreased from 282 to 270 k and also the saturation magnetization from 84 to 81 emu/g at 77 K. Mossbauer spectra of $La_{0.67}Ca_{0.33}Mn_{0.99}^{57}Fe_{0.01}O_3$ have been taken at various temperatures ranging form 4.2 K to room temperature. Analysis of $^{57}Fe$ Mossbauer data in terms of the local configurations of Mn atoms has permitted the influence of the magnetic hyperfine interactions to be monitored. The isomer shifts show that the charge state of all Fe ions are ferric. The magnetoresistance of $La_{0.67}Ca_{0.33}Mn_{0.99}^{57}Fe_{0.01}O_3$ was about 33 % at semiconductor-metal transition temperature $T_{SC-M}=250K$.

• Applied Chemistry for Engineering
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• v.32 no.5
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• pp.509-515
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• 2021

In this study, poly lactic-co-glycolic acid (PLGA) nanoparticles (PNP) were prepared through double (w/o/w) emlusion and emulsifying solvent-evaporation technique using PLGA, which has biocompatibility and biodegradability. To maximize stability and bioavailability of the particles, chitosan-coated PLGA nanoparticles (CPNP) were prepared by charge interaction between PNP and chitosan. We demonstrated that CPNP can be utilized as a drug carrier of oral administration. The chemical structure of CPNP was analyzed by ¹H-NMR and FT-IR, and all characteristic peaks appeared, confirming that it was successfully prepared. In addition, particle size and zeta potential of CPNP were analyzed using dynamic light scattering (DLS) while morphological images were obtained using transmission electron microscope (TEM). Thermal decomposition behavior of CPNP was observed through thermogravimetric analysis (TGA). In addition, the cytotoxicity of CPNP was confirmed by MTT assay at HEK293 and L929 cell lines, and it was proved that there is no toxicity confirmed by the cell viability of above 70% at all concentrations. These results suggest that the CPNP developed in this study may be used as an oral drug delivery carrier.

• Journal of the Korean Society of Radiology
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• v.15 no.2
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• pp.173-179
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• 2021

Scattered x-ray generated by digital radiography systems also have the advantage of increasing signals, but ultimately detectability is reduced by decreasing resolution and increasing noise of x-ray images transmitted objects. An indirect method of measuring scattered x-ray in a modulation-transfer function (MTF) for evaluating resolution in a spatial-frequency domain can be considered as a drop in the MTF value corresponding to zero-frequency. In this study, polymethyl methacrylate (PMMA) was used as a patient tissue equivalent, and MTFs were obtained for various thicknesses to quantify the effect of scattered x-ray on resolution. X-ray image signals were observed to decrease by 35 ~ 83% with PMMA thickness increasing, which is determined by the absorption or scattering of x-rays in PMMA, resulting in reduced MTF and increased scatter fraction. The method to compensate for MTF degradation by PMMA resulted in the MTF inflation without considering the optical spreading generated by the indirect-conversion type detector. Data fitting or zero-padding are needed to compensate for MTF more reasonably on edge-spread function or line-spread function.

• Korean Journal of Remote Sensing
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• v.37 no.2
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• pp.305-319
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• 2021

The overseas calibration sites such as Mongolia used for Korea Multi-purpose Satellite (KOMPSAT-5 or K5), have a disadvantage in that maintenance and repair costs are high and immediate response is difficult when an unexpected problem occurs. Accordingly, the necessity of establishing a domestic SAR calibration site was suggested, but the progress of related research is insignificant. In this paper, we investigated what conditions should be satisfied in terms of backscattering characteristics to construct a site for SAR satellite image quality evaluation and calibration. First of all, it was selected first by applying general indicators such as accessibility and availability among places recommended as satellite image calibration candidate sitesin Korea. Next, three places, site A (Goheung-gun, Jeollanam-do), site B (Jeonju-si, Jeollabuk-do), and site C (Daedeok Research Complex, Daejeon), were selected as the final candidates because they are relatively wide and easy to install AT or CR. Site A, located in Goheung-gun, Jeollanam-do, was best considered in terms of slope measurements, minimum site area to obtain ISLR, uniformity of DN values and backscatter coefficients, interference by strong reflectors, and backscatter clutter level.

• Economic and Environmental Geology
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• v.52 no.4
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• pp.313-322
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• 2019

SAR (Synthetic Aperture Radar) remote sensing data is a very useful tool for near-real-time identification of landslide affected areas that can occur over a large area due to heavy rains or typhoons. This study aims to develop an effective algorithm for automatically delineating landslide areas from the polarimetric SAR data acquired after the landslide event. To detect landslides from SAR observations, reduction of the speckle effects in the estimation of polarimetric SAR parameters and the orthorectification of geometric distortions on sloping terrain are essential processing steps. Based on the experimental analysis, it was found that the IDAN filter can provide a better estimation of the polarimetric parameters. In addition, it was appropriate to apply orthorectification process after estimating polarimetric parameters in the slant range domain. Furthermore, it was found that the polarimetric entropy is the most appropriate parameters among various polarimetric parameters. Based on those analyses, we proposed an automatic landslide detection algorithm using the histogram thresholding of the polarimetric parameters with the aid of terrain slope information. The landslide detection algorithm was applied to the ALOS-2 PALSAR-2 data which observed landslide areas in Japan triggered by Typhoon in September 2011. Experimental results showed that the landslide areas were successfully identified by using the proposed algorithm with a detection rate of about 82% and a false alarm rate of about 3%.

• Journal of the Korea Society for Simulation
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• v.28 no.2
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• pp.139-147
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• 2019

A MANPADS(Man Portable Air Defense System), which tracks infrared energy, is light enough for individuals to carry and can against to a variety of aircraft, making it widely deployed around the world, posing a major threat to aircraft. A flare has been developed as an IRCM(Infrared Countermeasures) that protects the life of friendly aircraft and combatants by deceiving such guided missiles. However, DIRCM, which can overcome the problems of existing IRCM, is being developed mainly in some developed countries, and the need for it has been increasing gradually. This paper modeled first generation IR seeker of AM modulation method, the second generation IR seeker of FM modulation method, and the third generation IR seeker of pulse modulation method among various MANPADS, and modeled the scattering light phenomenon in the seeker when laser beams are investigated in DIRCM. Using this, jamming simulations were performed in various engagement environments of the MANPADS and aircraft equipped with DIRCM, and the miss distance of the guided missiles and aircraft were analyzed. Simulation results show that DIRCM, which irradiates a modulated laser beam with one jamming code, deceives both first, second and third generation MANPADS at 1km and 2km of engagement distance. In particular, the survival rate of aircraft equipped with DIRCM increased when the distance of engagement increased from 1km to 2km, and the survival rate was at least 99% at 2km of engagement distance.

• Particle and aerosol research
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• v.16 no.4
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• pp.131-140
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• 2020

Air pollutants emitted from chimneys of coal-fired power plants are considered to be a major source of fine particulate matter in the atmosphere. In order to manage fine particle in the chimney of a coal-fired power plant, it is necessary to know the concentration of fine particle emitted in real time, but the current system is difficult. In this study, a real-time measurement system for chimney fine particle was developed, and measurements were performed on six coal-fired power plants. Through the measurements, the mass concentration distribution according to the particle size could be secured. All six chimneys showed bimodal distribution, and the count median diameters of each mode were 0.5 and 1.1 ㎛. In addition, it was compared with the gravimetric measurement method, and it was determined that the relative accuracy for PM10 was within 20%, and the value measured using the developed measuring instrument was reliable. Finally, three power plants were continuously measured for one month, and as a result of comparing the concentration of PM10 according to the amount of power generation, it was confirmed that the PM10 discharged from the chimney increased in the form of an exponential function according to the amount of power generation.