• Current Applied Physics
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• 제18권11호
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• pp.1403-1409
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• 2018

In the present study, the $SrMoO_4:Eu^{3+}$ phosphors has been synthesized through hydro-thermal co-precipitation method, and single factor and orthogonal experiment method was adopted to find optimal synthesis condition. It is interesting to note that hydro-thermal temperature is a prominent effect on the luminescent intensity of $SrMoO_4:Eu^{3+}$ red phosphor, followed by co-precipitation temperature, calcining time, and the doping amount of $Eu^{3+}$. The optimal synthesis conditions were obtained: hydro-thermal temperature is $145^{\circ}C$, co-precipitation temperature is $35^{\circ}C$, the calcining time is 2.5 h, and the doping amount of activator $Eu^{3+}$ is 25%. Subsequently, the crystalline particle size, phase composition and morphology of the synthesized phosphors were evaluated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results show that these phosphors possess a scheelite-type tetragonal structure, and the particle size is about $0.2{\mu}m$. Spectroscopic investigations of the synthesized phosphors are carried out with the help of photo-luminescence excitation and emission analysis. The studies reveal that $SrMoO_4:Eu^{3+}$ phosphor efficiently convert radiation of 394 nm-592 and 616 nm for red light, and the luminescence intensity of $SrMoO_4:Eu^{3+}$ phosphors is improved. $SrMoO_4:Eu^{3+}$ phosphors may be a potential application for enhancing the efficiency of white LEDs.

• 대한금속재료학회지
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• 제46권10호
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• pp.672-682
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• 2008

The resistance spot welding of TRIP590 steels was investigated to enhance understanding of weld fracture during tensile-shear strength (TSS) test. The main failure modes for spot welds of TRIP590 steels were nugget pullout and interfacial fracture. The peak load to cause a weld interfacial failure was found to be related to fracture toughness of the weld and the weld diameter. Although interfacial fracture occurred in the samples, the load carrying capacity of the weld was high and not significantly affected by the fracture mode. Substantial part of the weld exhibits the characteristic dimple (or elongated dimple) fractures on interfacial fractured surface, in spite of the high hardness values associated with the martensite microstructures. The high load-bearing ability of the weld is directly associated with the area of ductile fracture occurred in weld. Therefore, the judgment of the quality of resistance spot welds in TRIP590 steels, the load carrying capacity of the weld should be considered as an important factor than fracture mode.

• 터널과지하공간
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• 제31권6호
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• pp.508-519
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• 2021

본 연구에서는 발파 시 사람과 주변 환경에 영향을 끼치는 발파진동(peak particle velocity, PPV)을 예측하는 모델을 개발하였다. PPV를 예측하기 위해 kNN(k-nearest neighbors), CART(classification and regression tree), SVR(support vector regression), PSO(particle swarm optimization)-SVR 알고리즘을 이용한 4가지 머신러닝 모델을 개발하고 상호 비교하였다. 머신러닝 모델을 훈련하기 위해 경상남도 창원시에 있는 욕망산을 연구지역으로 선정하고 1048개의 발파 데이터를 획득하였다. 발파 데이터는 천공장, 저항선, 공간격, 최대지발장약량, 비장약량, 총공수, 에멀전비율, 이격거리, PPV로 구성되었다. 훈련된 모델들의 성능을 평가하기 위한 지표 값으로 MAE(mean absolute error), MSE(mean squared error), RMSE(root mean squared error)를 사용하였다. 평가결과 PSO-SVR 모델이 MAE, MSE, RMSE가 각각 0.0348, 0.0021, 0.0458으로 가장 우수한 예측 성능을 나타냈다. 마지막으로 개발된 머신러닝 모델을 이용하여 주변 환경에 영향을 끼치는 정도를 예측하는 방법을 제시하였다.

• Journal of Ginseng Research
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• 제46권6호
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• pp.809-818
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• 2022

Background: The non-saponin fraction (NSF) of Korean Red Ginseng is a powder in which saponin is eliminated from red ginseng concentrate by fractionation. In this study, we examined the effect of NSF on age-associated sarcopenia in old mice. Methods: NSF (50 or 200 mg/kg/day) was administered orally daily to young (3-6-month-old) and old (20-24-month-old) C57BL/6 J mice for 6 weeks. Body weight and grip strength were assessed once a week during the oral administration period. The gastrocnemius and quadriceps muscle were excised, and the muscle fiber size was compared through hematoxylin and eosin staining. In addition, the effect of NSF on sarcopenia and inflammation/oxidative stress-related factors in hindlimb muscles was investigated by western blotting. Flow cytometry analysis was conducted to investigate the effect of NSF on immune homeostasis. Blood samples were collected by cardiac puncture, and the serum levels of insulin-like growth factor 1, pro-inflammatory cytokines, and glutathione were evaluated. Results: NSF significantly alleviated muscle strength, mass, and also fiber size in old mice. Age-associated impairment of immune homeostasis was recovered by NSF through retaining CD11b⁺F4/80⁺ macrophages and regulating inflammatory biomarkers. NSF also decreased the age-induced expression of oxidative stress factors. Taken together, NSF showed the effect of improving sarcopenia by inhibiting low-grade chronic inflammatory/oxidative stress factors. Conclusion: NSF exhibited anti-sarcopenia effects by regulating chronic inflammation and oxidative stress in old mice. Thus, we suggest that NSF is a promising restorative agent that can be used to improve sarcopenia in the elderly as well as maintain immune homeostasis.

• 한국재료학회지
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• 제33권7호
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• pp.295-301
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• 2023

Thermoelectric (TE) energy harvesting, which converts available thermal resources into electrical energy, is attracting significant attention, as it facilitates wireless and self-powered electronics. Recently, as demand for portable/wearable electronic devices and sensors increases, organic-inorganic TE films with polymeric matrix are being studied to realize flexible thermoelectric energy harvesters (f-TEHs). Here, we developed flexible organic-inorganic TE films with p-type Bi_0.5Sb_1.5Te₃ powder and polymeric matrices such as poly(3,4-eethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and poly (vinylidene fluoride) (PVDF). The fabricated TE films with a PEDOT:PSS matrix and 1 wt% of multi-walled carbon nanotube (MWCNT) exhibited a power factor value of 3.96 µW·m^-1·K^-2 which is about 2.8 times higher than that of PVDF-based TE film. We also fabricated f-TEHs using both types of TE films and investigated the TE output performance. The f-TEH made of PEDOT:PSS-based TE films harvested the maximum load voltage of 3.4 mV, with a load current of 17.4 µA, and output power of 15.7 nW at a temperature difference of 25 K, whereas the f-TEH with PVDF-based TE films generated values of 0.6 mV, 3.3 µA, and 0.54 nW. This study will broaden the fields of the research on methods to improve TE efficiency and the development of flexible organic-inorganic TE films and f-TEH.

• 한국재료학회지
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• 제33권7호
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• pp.285-294
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• 2023

Porous ceramics are used in various industrial applications based on their physical properties, including isolation, storage, and thermal barrier properties. However, traditional manufacturing environments require additional steps to control artificial pores and limit deformities, because they rely on limited molding methods. To overcome this drawback, many studies have recently focused on fabricating porous structures using additive manufacturing techniques. In particular, the binder jet technology enables high porosity and various types of designs, and avoids the limitations of existing manufacturing processes. In this study, we investigated process optimization for manufacturing porous ceramic filters using the binder jet technology. In binder jet technology, the flowability of the powder used as the base material is an important factor, as well as compatibility with the binder in the process and for the final print. Flow agents and secondary binders were used to optimize the flowability and compatibility of the powders. In addition, the effects of the amount of added glass frit, and changes in sintering temperature on the microstructure, porosity and mechanical properties of the final printed product were investigated.

• 한국환경농학회지
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• 제42권4호
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• pp.338-345
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• 2023

Bacillus spp. and Saccharomyces spp. are effective microorganisms that are applied as microbial fertilizers for crops in Korea. Mixed organic fertilizer (MOF) has been used in the Korean organic agriculture to supply nutrients to crops. This study was conducted to investigate the effects of MOF containing Bacillus amyloliquefaciens HSOB-7 and Saccharomyces cerevisiae HSOB-8 (MOFBS) on the soil chemical properties and growth of lettuce (Lactuca sativa). Growth factors of lettuce were higher after applying different formulation types of MOFBS, such as powder and pellet, than those of NF, and not significantly different than those of control (microbe-free MOF). Compared with the control, application of recommended amount of MOFBS (MOFBS 250 kg/10a, MOFBS treatment) and double the recommended amount (MOFBS 500 kg/10a, 2MOFBS treatment) did not significantly change the growth factors of lettuce. After the application of two formulation types or two different amounts of MOFBS, soil chemical properties such as electrical conductivity, organic matter (OM), exchangeable Ca, and cation exchangeable cation (CEC) increased. These results indicated that although the application of MOFBS improved soil fertility including OM and CEC, it did not significantly affect lettuce growth.

• 한국건축시공학회지
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• 제23권6호
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• pp.727-738
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• 2023

계면은 콘크리트 강도 결정 요인 중 가장 약한 영역으로, 골재와 시멘트 페이스트 사이에서 형성된다. 경량골재는 원재료를 팽창, 소성시켜 제조하기 때문에 표면에 수많은 공극을 형성하여 밀도가 낮은 장점을 지니지만 골재 강도가 약하다. 콘크리트는 골재강도가 약하면 골재의 파단이 발생한다. 경량골재의 콘크리트 적용은 골재 파단 때문으로 계면의 강도가 중요하다. 본 연구에서는 경량골재의 계면강도 증진을 위해 고로슬래그 미분말로 골재표면을 코팅하고, 시험체의 임피던스를 비교하여 표면개질에 의한 계면 변화를 분석하였다. 실험결과, 경량골재 표면코팅 시 압축강도가 약 4%정도 증가하였고, 강도 증가에 따라 임피던스 값 중 레지스턴스 값이 증가하는 것을 확인하였다.

• 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.

• 마이크로전자및패키징학회지
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• 제18권4호
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• pp.55-61
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• 2011

n형 $Bi_2(Te_{0.9}Se_{0.1})_3$ 분말을 기계적 합금화 공정으로 제조하고 텅스텐 분말을 분산시켜 $550^{\circ}C$에서 30분간 가압소결 후, 텅스텐 함량에 따른 열전특성을 분석하였다. 텅스텐 분말을 분산시키지 않은 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체의 상온 출력인자는 $21.9{\times}10^{-4}$ $W/m-K^2$ 이었으며, 1 vol% 텅스텐 분말의 분산에 의해 상온 출력인자가 $30.5{\times}10^{-4}$ $W/m-K^2$로 증가하였다. 텅스텐 분말을 분산시키지 않은 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체는 상온에서 0.52의 무차원 성능지수를 나타내었으며, 1 vol% 텅스텐 분말의 분산에 의해 무차원 성능지수가 0.95로 크게 향상되었다.