• Korea Journal of Cosmetic Science
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• 제2권1호
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• pp.1-10
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• 2020

Protection mechanisms for skin damage of ultraviolet (UV) absorbers in personal care products for protection against UV are well studied, but not for hair protection. The purpose of this study is to describe and compare the changes of physical property produced in human hair by doses of the UV-B exposure causing protein degradation. To observe the change of physical properties in hair, the experimental intensity of UV-B exposure has been established on the basis of statistical data from official meterological administration as daily one hour sunlight exposure for two weeks. Polysilicone-15, ethylhexyl methoxycinnamate (OMC), and octocrylene were employed for UV-B absorber, and those were treated to hair swatch by rubbing wash through shampoo and conditioner. Bending rigidity displayed kinetically successive reduction at high doses of UV exposure up to the 8,000 s, and exhibited different level at each sample of UV-B absorber. However, the values of Bossa Nova Technologies (BNT) for shinning factor were already saturable at the 2,000 s exposure except that treated with polysilicone-15. The differential scanning calorimetry (DSC) to measure a strength of inner protein produces a successive reduction of enthalpy as like a reduction of bending rigidity upon UV exposure. Surface roughness from lateral force microscope (LFM) acquired immediately after UV exposure show a saturable frictional voltage which has been also found in a saturable BNT data as the time of UV exposure increases. Through researching the DSC and the LFM, shinning of hair was much correlated to the protein damage at the surface, and bending rigidity could be regulated by the protein structural damage inside hair. Therefore, the optimization of efficient strategy for simultaneous prevention of hair protein on the surface and internal hair was required to maintain physical properties against UV.

• 한국재료학회지
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• 제31권11호
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• pp.619-625
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• 2021

Cu₂ZnSn(S,Se)₄ (CZTSSe) based thin-film solar cells have attracted growing attention because of their earth-abundant and non-toxic elements. However, because of their large open-circuit voltage (V_oc)-deficit, CZTSSe solar cells exhibit poor device performance compared to well-established Cu(In,Ga)(S,Se)₂ (CIGS) and CdTe based solar cells. One of the main causes of this large V_oc-deficit is poor absorber properties for example, high band tailing properties, defects, secondary phases, carrier recombination, etc. In particular, the fabrication of absorbers using physical methods results in poor surface morphology, such as pin-holes and voids. To overcome this problem and form large and homogeneous CZTSSe grains, CZTSSe based absorber layers are prepared by a sputtering technique with different RTA conditions. The temperature is varied from 510 ℃ to 540 ℃ during the rapid thermal annealing (RTA) process. Further, CZTSSe thin films are examined with X-ray diffraction, X-ray fluorescence, Raman spectroscopy, IPCE, Energy dispersive spectroscopy and Scanning electron microscopy techniques. The present work shows that Cu-based secondary phase formation can be suppressed in the CZTSSe absorber layer at an optimum RTA condition.

• 한국재료학회지
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• 제32권5호
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• pp.243-248
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• 2022

This study demonstrates a different approach method to fabricate antimony selenide (Sb₂Se₃) thin-films for the solar cell applications. As-deposited Sb₂Se₃ thin-films are fabricated via electrodeposition route and, subsequently, annealed in the temperature range of 230 ~ 310℃. Cyclic voltammetry is performed to investigate the electrochemical behavior of the Sb and Se ions. The deposition potential of the Sb₂Se₃ thin films is determined to be -0.6 V vs. Ag/AgCl (in 1 M KCl), where the stoichiometric composition of Sb₂Se₃ appeared. It is found that the crystal orientations of Sb₂Se₃ thin-films are largely dependent on the annealing temperature. At an annealing temperature of 250 ℃, the Sb₂Se₃ thin-film grew most along the c-axis [(211) and/or (221)] direction, which resulted in the smooth movement of carriers, thereby increasing the carrier collection probability. Therefore, the solar cell using Sb₂Se₃ thin-film annealed at 250 ℃ exhibited significant enhancement in J_SC of 10.03 mA/cm² and a highest conversion efficiency of 0.821 % because of the preferred orientation of the Sb₂Se₃ thin film.

• Wind and Structures
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• 제36권2호
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• pp.91-103
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• 2023

Tuned liquid dampers (TLDs) are increasingly being used as efficient dynamic vibration absorbers to mitigate wind-induced vibration in super high-rise buildings. However, the damping characteristics of screens and the control effectiveness of actual structures must be investigated to improve the reliability of TLDs in engineering applications. In this study, a numerical TLD model is developed using computational fluid dynamics (CFD) and a simulation method for achieving the coupled vibration of the structure and TLD is proposed. The numerical results are verified using shaking table tests, and the effects of the solidity ratio and screen position on the TLD damping ratios are investigated. The TLD control effectiveness is obtained by simulating the wind-induced vibration response of a full-scale structure-TLD system to determine the optimal screen solidity ratio. The effects of the structural frequency, damping ratio, and wind load amplitude on the TLD performance are further analyzed. The TLD damping ratio increases nonlinearly with the solidity ratio, and it increases with the screens towards the tank center and then decreases slightly owing to the hydrodynamic interaction between screens. Full-scale coupled simulations demonstrated that the optimal TLD control effectiveness was achieved when the solidity ratio was 0.46. In addition, structural frequency shifts can significantly weaken the TLD performance. The control effectiveness decreases with an increase in the structural damping ratio, and is insensitive to the wind load amplitude within a certain range, implying that the TLD has a stable damping performance over a range of wind speed variations.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2578-2590
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• 2023

In this work, a 24-month two-batch fuel management strategy for the APR1400 using LEU + has been investigated, where enrichments of 5.9 and 5.2 w/o are utilized in lieu of the conventional 4-5 w/o UO₂ fuel. In addition, an Accident Tolerant Fuel (ATF) clad based on the swaging technology is applied to APR1400 fuel assemblies. In this special ATF clad design, both outer and inner SS316 layers protect the conventional zircaloy clad. Erbia (Er₂O₃) is introduced as a burnable absorber with two-fold goals to lower the critical boron concentration in the long-cycle LEU + loaded core as well as to handle the LEU + fuel in the existing front-end fuel facilities without renewing the license. Two types of fuel assemblies with different loading of gadolinia (Gd₂O₃) are considered to control both the reactivity and the core radial power distribution. The erbia burnable absorber is uniformly admixed with UO₂ in all fuel pins except for the gadolinia-bearing ones. In this study, two core designs were devised with different erbia loading, and core performance and safety parameters were evaluated for each case in comparison with a core design without any burnable absorbers. The core analysis was done using the two-step method. First, cross-sections are generated by the SERPENT 2 Monte Carlo code, and the 3-D neutronic analysis is performed with an in-house multi-physics nodal code KANT.

• Current Optics and Photonics
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• 제7권6호
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• pp.738-744
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• 2023

Graphene-based saturable absorbers (SAs) are widely used as laser mode-lockers at various laser oscillators. In particular, transmission-type graphene-SAs with ultrabroad spectral coverage are typically manufactured on transparent substrates with low nonlinearity to minimize the effects on the oscillators. Here, we developed two types of transmitting graphene SAs based on CaF₂ and ZnSe. Using the graphene-SA based on CaF₂, a passively mode-locked mid-infrared Cr:ZnS laser delivers relatively long 540 fs pulses with a maximum output power of up to 760 mW. In the negative net cavity dispersion regime, the pulse width was not reduced further by inhomogeneous group delay dispersion (GDD) compensation. In the same laser cavity, we replaced only the graphene-SA based on CaF₂ with the SA based on ZnSe. Due to the additional self-phase modulation effect induced by the ZnSe substrate with high nonlinearity, the stably mode-locked Cr:ZnS laser produced Fourier transform-limited ~130 fs near 2,340 nm. In the stable single-pulse operation regime, average output powers up to 635 mW at 234 MHz repetition rates were achieved. To our knowledge, this is the first attempt to achieve shorter pulse widths from a polycrystalline Cr:ZnS laser by utilizing the graphene deposited on the substrate with high nonlinearity.

• 한국응용과학기술학회지
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• 제32권2호
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• pp.339-347
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• 2015

본 연구는 멀티플 에멀젼(W/O/W) 시스템을 이용하여 개발한 자외선차단 제품의 자외선차단성능의 지속성과 보습효과에 관한 연구이다. 자외선차단용 화장품은 장시간의 외출, 등산, 레포츠 활동을 할 때 필수적으로 사용하는 제품으로 높은 자외선차단효과와 지속성이 요구되고 있다. 또한, 소비자들은 감성공학적인 측면에서 끈적이지 않으며, 내수성이 우수한 제품을 선호하고 있다. 친수성 (O/W타입) 자외선차단제품의 경우, 사용감은 우수하나, 땀이나, 물에 쉽게 지워지기 때문에 완벽한 자외선차단 효과를 기대할 수 없으며, 내수성이 우수한 친유형 (W/O타입) 제품의 경우, 내수성은 우수하나, 끈적임이 심하고, 보습효과가 낮다. 따라서 본 연구에서는 멀티플에멀젼(W/O/W)시스템의 퍼뮬레이션을 개발하여 친수성크림의 부드럽고 촉촉한 사용감을 부여하고 흡수 후에는 내수성이 우수한 W/O 제형으로 변화하여, 우수한 내수성과 자외선차단효과의 지속성을 가지는 고기능성 다중에멀젼의 자외선차단크림을 개발하는 것이 목적이다. 자외선차단크림에 사용된 성분으로 UV-B를 차단하는 원료 에칠헥실메톡시 신나메이트, 이소아밀-p-메톡시신나메이트, 에틸헥실살리실레이트, 옥토크릴렌을 사용하였으며, UV-A차단제로 부틸메톡시디벤조일메탄과 비스에칠헥실옥시페놀 메톡시페닐트리아진을 사용하였다. O/W형 크림의 자외선차단효과를 나타내는 SPF 수치가 34.1, W/O/W형 크림에서는 SPF 수치가 40.6으로, O/W형 크림보다는 19%정도 자외선 차단효과가 상승하는 것으로 나타났다. 4시간 경과 후의 내수성시험에서는 O/W형 크림의 경우 자외선차단효과가 3.6정도로 30.5이상 하락하였으나, 다중에멀젼 시스템에서는 자외선차단효과가 32.7로, 7.9정도 하락하여 81%의 내수성이 있는 것으로 나타났다. 사용 30분 후의 보습효과는 친수성크림이 우수하였으나, 3시간 이후의 보습력은 멀티플에멀젼에서 더욱 높은 보습효과를 보였다.

• 한국전자파학회논문지
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• 제26권10호
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• pp.841-850
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• 2015

전자 및 전파 통신기술의 급속한 발전에 따라 인류는 정보통신의 커다란 혜택을 누릴 수 있게 되었다. 그러나 전자파환경은 보다 복잡해지고, 각종 전자기기를 비롯한 인체에 다양한 영향을 미치게 되어 ANSI, FCC, CISPR 등과 같은 국제기구에서는 다양한 전자파환경을 규제하고, 효율적인 제어 및 대책을 수립해 오고 있다. 본 논문에서는 방열 기능을 가지면서 고성능의 전파흡수체 제조 방법을 제안하고, 나아가 미래의 스마트 전파흡수체의 전망을 기술하였다. 산화철($Fe_2O_3$)과 세라믹의 혼합물을 고온 열처리한 후, 탄소 물질과 배합하여 저온 열처리하고, 개구를 형성하여 2~2.45 GHz에서 방열 기능을 가지면서 흡수능이 20 dB 이상인 고성능 전파흡수체를 개발하였다. 이 스마트 전파흡수체는 다양한 전자, 통신, 제어, 전파 시스템의 회로 및 부품 보호용 소재로 활용성이 높을 것으로 보인다.

• 대한기계학회논문집B
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• 제35권3호
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• pp.229-235
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• 2011

본 연구는 암모니아/물 혼합냉매를 이용한 압축/흡수식하이브리드 히트펌프 개발에 관한 연구이다. 히트펌프 사이클은 증기압축식과흡수식을 혼합한 개념으로 이단압축기, 흡수기, 재생기, 과열냉각기, 용액열교환기(SHX), 용액펌프, 정류기, 기액분리기 등으로 구성되어 있다. 압축/흡수식 히트펌프는 상변화 열교환과정에서 높은 온도구배를 이용하여 $90^{\circ}C$ 이상의 고온을 제조하기 위한 목적으로 고안되었다. 특히 흡수기에서의 응축과정은 비열변화로 인하여 온도변화에 비선형성이 뚜렷한데, 시스템 성능 최적화를 위하여는 흡수기의 설계가 중요하다. 본 연구에서는 다수의 판형열교환기로 흡수기를 구성하였는데 열교환기의 용량, 형태, 배치에 따른 성능특성을 실험적으로 관찰하였다.

• 한국재료학회지
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• 제4권1호
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• pp.3-8
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• 1994

최근 중요하게 된 진동 흡수를 위해서 $BaTiO_{3}$ 세라믹의 흡진 특성을 측정하고 미세구조와의 연관을 조사했다.$BaTiO_{3}$ 세라믹은 비교적 물리적 화학적으로 안정하여 좋은 흡진재로 기대된다.BaTiO$_{3}$ 세라믹은 흡진 특성을 강화시키기 위해서 섬유상 분말을 소결하여 만들었다. KDC법으로 직경이 0.2$\mu\textrm{m}$, 1.2$\mu\textrm{m}$, 2.0$\mu\textrm{m}$인 각각 다른 섬유상 $K_2Ti_4O_9$을 만들고 이온교환해서 섬유상 $BaTiO_{3}$ 을 만들었다. 면상으로 배향시킨 소결체의 흡진 특성과 전기적 물성을 조사하여 미세구조와 의 관계를 밝혔다. 소결체의 입경과 등가회로, 전기기계합계수($K_{t}$), 발생 전압(V)을 조사한 결과, 사용한 섬유의 직경이 클수록 소결체의 입경은 작아졌다. 따라서 입계가 많아졌다. 흡진 특성은 입계가 많을수록 커진다. 즉 입계의 내무마찰이 클수록 흡진률은 커지며 이때의 내부마찰은 등가회로를 조사함으로써 확인되었다.