• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.99.1-99.1
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• 2012

The thin-film photovoltaic absorbers (CdTe and $Cu(In,Ga)Se_2$) can achieve solar conversion efficiencies of up to 20% and are now commercially available, but the presence of toxic (Cd,Se) and expensive elemental components (In, Te) is a real issue as the demand for photovoltaics rapidly increases. To overcome these limitations, there has been substantial interest in developing viable alternative materials, such as $Cu_2ZnSnS_4$ (CZTS) is an emerging solar absorber that is structurally similar to CIGS, but contains only earth abundant, non-toxic elements and has a near optimal direct band gap energy of 1.4 - 1.6 eV and a large absorption coefficient of ~104 $cm^{-1}$. The CZTS absorber layers are grown and investigated by various fabrication methods, such as thermal evaporation, e-beam evaporation with a post sulfurization, sputtering, non-vacuum sol-gel, pulsed laser, spray-pyrolysis method and electrodeposition technique. In the present work, we report an alternative aqueous chemical approach based on chemical bath deposition (CBD) method for large area deposition of CZTS thin films. Samples produced by our method were analyzed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, absorbance and photoluminescence. The results show that this inexpensive and relatively benign process produces thin films of CZTS exhibiting uniform composition, kesterite crystal structure, and some factors like triethanolamine, ammonia, temperature which strongly affect on the morphology of CZTS film.

• Journal of Powder Materials
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• v.25 no.5
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• pp.415-419
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• 2018

Porous metals demonstrate not only excessively low densities, but also novel physical, thermal, mechanical, electrical, and acoustic properties. Thus, porous metals exhibit exceptional performance, which are useful for diesel particulate filters, heat exchangers, and noise absorbers. In this study, SUS316L foam with 90% porosity and $3,000{\mu}m$ pore size is successfully manufactured using the electrostatic powder coating (ESPC) process. The mean size of SUS316L powders is approximately $12.33{\mu}m$. The pore properties are evaluated using SEM and Archimedes. As the quantity of powder coating increases, pore size decreases from 2,881 to $1,356{\mu}m$. Moreover, the strut thickness and apparent density increase from 423.7 to $898.3{\mu}m$ and from 0.278 to $0.840g/cm^3$, respectively. It demonstrates that pore properties of SUS316L powder porous metal are controllable by template type and quantity of powder coating.

• The Korean Journal of Physiology and Pharmacology
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• v.19 no.3
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• pp.241-247
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• 2015

Ultraviolet (UV) radiation-induced loss of dermal extracellular matrix is associated with skin photoaging. Recent studies demonstrated that keratinocyte-releasable stratifin (SFN) plays a critical role in skin collagen metabolism by inducing matrix metalloproteinase 1 (MMP1) expression in target fibroblasts. In the present study, we examined whether SFN released from UVB-irradiated epidermal keratinocytes increases MMP1 release from dermal fibroblasts, and whether these events are affected by p-coumaric acid (p-CA), a natural phenolic compound with UVB-shielding and antioxidant properties. HaCaT cells were exposed to UVB in the absence and presence of p-CA, and the conditioned medium was used to stimulate fibroblasts in medium transfer experiments. The cells and media were analyzed to determine the expressions/releases of SFN and MMP1. UVB exposure increased SFN release from keratinocytes into the medium. The conditioned medium of UVB-irradiated keratinocytes increased MMP1 release from fibroblasts. The depletion of SFN using a siRNA rendered the conditioned medium of UVB-irradiated keratinocytes ineffective at stimulating fibroblasts to release MMP1. p-CA mitigated UVB-induced SFN expression in keratinocytes, and attenuated the MMP1 release by fibroblasts in medium transfer experiments. In conclusion, the present study demonstrated that the use of UV absorbers such as p-CA would reduce UV-induced SFN-centered signaling events involved in skin photoaging.

• Journal of the Korean Magnetics Society
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• v.17 no.6
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• pp.238-241
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• 2007

Ni-Cu-Zn ferrites were prepared by the co-precipitation. Physical properties and Microwave absorbing properties were investigated in Ni-Cu-Zn ferrite for the aim of microwave absorbers. From the analysis of X-ray diffraction patterns, we can see that all the particles have only a single phase spinel structure. The loss factor was maximum at sintering temperature $1100^{\circ}C$. The initial permeability of sintered ferrite obtained was an average of 50. We found that the $(Ni_{0.7}Cu_{0.2}Zn_{0.1}O)_{1.02}(Fe_2O_3)_{0.98}$ can be used in ferrite rubber composite microwave absorber when sintering temperature at $1100^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.115-119
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• 2008

The raw materials of permalloy were processed the ball-mill for 30 hours and the shape of permalloy particles was changed from sphere to flake type, which was observed using scanning electron microscope. The complex permittivity and permeability spectra and reflection loss of permalloy-rubber composite was measured using Network Analyzer in order to investigate the relationship between the microwave absorption and the material constants. The flake type permalloy-rubber composite showed high reflection loss, which was due to the high complex permittivity and permeability. Also, the matching frequency shifted toward lower frequency range with microwave absorber thickness, and the maximum reflection loss of -6.1 dB was observed in $1.65\;GHz{\sim}1.86\;GHz$ for a 1.3 mm thickness.

• Journal of Radiation Protection and Research
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• v.18 no.2
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• pp.47-59
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• 1993

The criticality of the shipping cask(KSC-7) for transportion of 7PWR spent fuel assemblies has been calculated and analysised on the basis of neutron transport theory. For criticality analysis, effects of the rod pitches, the fixed neutron absorbers(borated sus+boral) were considered. The effective multiplication factor has been calculated by KENO-Va, Mote Carlo method computer code, with the HANSEN-ROACH 16 group cross section set, which was made for personal computer system. The criticality for the KSC-7 cask was calculated in terms of the fresh fuel which was conservative for the aspects of nuclear critility. From the results of criticality analysis, the calculated Keff is proved to be lower than subcritical limit during normal transportation and under hypothetical accident condition. The maximum calculated criticalities of the KSC-7 were lower the safety criticality limit 1.0 recommended by US 10CFR71 both under normal and hypothetical accident condition. Also, to verify the KSC-7 criticality calculation results by using KENO-Va, it was carried out benchmark calculation with experimental data of B & W(Bobcock and Wilcox) company. From the 3s series of calculation of the KSC-7 cask and benchmark calculation, the cask was safely designed in nuclear criticality, respectively.

• Journal of Navigation and Port Research
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• v.33 no.3
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• pp.193-197
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• 2009

In this paper, the EM wave absorber was designed and fabricated for improvement of Wireless LAN environment at 2.4 GHz. We fabricated several samples in different composition ratios of Sendust and CPE(Chlorinated Polyethylene). Absorption abilities were simulated in accordance with different thicknesses of the prepared absorbers and changed complex relative permittivity and permeability due to composition ratio. The mixing ratio of Sendust and CPE was searched as 80: 20 wt.% by experiments and simulation Then the EM wave absorber was fabricated and tested using the simulated data. As a result, the EM wave absorber was fabricated based on simulated data. Simulated and measured results agreed well. As a result, the developed EM wave absorber with thickness of 3.25 mm has absorption ability of 19 dB at 2.4 GHz.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.4
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• pp.121-128
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• 2005

In most researches on the ride comfort analysis of passenger vehicles, the flexibility of the vehicle body has been not considered as an important factor, because the resonance frequencies of the vehicle body related to pitching, yawing and rolling motions are below 10Hz while the resonance frequencies of the vehicle body related to the flexibility are above 20Hz approximately. Nevertheless, the paper shows that the consideration of the local flexibility (or local stiffness) of the 4 corners on which shock absorbers are mounted influences the ride comfort. A simple beam model is devised to qualitatively examine the effect of the change of the local stiffness of the vehicle body on the ride comfort. Based on the results obtained from the analysis of the one-dimensional model, multi-body dynamic analysis considering the flexibility of the vehicle body is performed using ADAMS and MSC/NASTRAN. Natural frequencies and mode shapes computed by MSC/NASTRAN are used as input data for multi-body dynamic analysis in ADAMS. Through simulations using ADAMS, it has been found that the ride comfort can be improved by changing the local stiffness of the vehicle body and that the simulation results agree with experiment results.

• Nuclear Engineering and Technology
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• v.52 no.1
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• pp.19-26
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• 2020

Small nuclear reactor features higher power capacity, longer operation life than conventional power sources. It could be an ideal alternative of existing power source applied for special equipment for terrestrial or underwater missions. In this paper, a 25kWe heat pipe cooled reactor power source applied for multiple use is preliminary designed. Based on the design, a thermal-hydraulic analysis code for heat pipe cooled reactor is developed to analyze steady and transient performance of the designed nuclear reactor. For reactor design, UN fuel with 65% enrichment and potassium heat pipes are adopted in the reactor core. Tungsten and LiH are adopted as radiation shield on both sides of the reactor core. The reactor is controlled by 6 control drums with B₄C neutron absorbers. Thermoelectric generator (TEG) converts fission heat into electricity. Cooling water removes waste heat out of the reactor. The thermal-hydraulic characteristics of heat pipes are simulated using thermal resistance network method. Thermal parameters of steady and transient conditions, such as the temperature distribution of every key components are obtained. Then the postulated reactor accidents for heat pipe cooled reactor, including power variation, single heat pipe failure and cooling channel blockage, are analyzed and evaluated. Results show that all the designed parameters satisfy the safety requirements. This work could provide reference to the design and application of the heat pipe cooled nuclear power source.

• Korean Journal of Materials Research
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• v.18 no.10
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• pp.564-570
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• 2008

Nanostructured carbon materials have been found to have applications in fuel cell electrodes, field emitters, electronic devices, sensors and electromagnetic absorbers, etc. Especially, the CNF (carbon nanofiber) can be expected to play an important role in catalyst supporters for fuel cell electrodes and chemical reactions. In this study, we synthesized CNF from a liquid phase carbon source by a solvothermal method. In addition, we studied the parameters for the preparation of CNF by controlling heating and cooling rates, synthesis temperature and time. We characterized the CNF by SEM/TEM, XRD, Raman spectroscopy and EDS. We found that the heating and cooling rate have strong effects on the CNF formation and growth. We were able to prepare the best CNF at the heating rate of $10^{\circ}$/min, at $450^{\circ}$ for 60 minutes, and at the cooling rate of $4^{\circ}$/min. As a result of Raman spectra, we found that the sample showed two characteristic Raman bands at ${\sim}1350cm^{-1}$ (D band) and ${\sim}1600cm^{-1}$ (G band). The G band indicates the original graphite feature, but the D band has been explained as a disorder feature of the carbon structure. The diameter and length of the CNF was about $15{\sim}20nm$, and over $1{\mu}$, respectively.