• 대한안전경영과학회지
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• 제25권2호
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• pp.153-158
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• 2023

This research was conducted to reduce the defect rate caused by nozzle clogging of printing heads used in binder jet 3D printers. The binder jet 3D printing technology may adhere to the printing head nozzle by dispersing powder due to mechanical operation such as transferring the printing head and supplying powder, and may cause nozzle clogging by natural curing at the nozzle end depending on the type of binder used. To solve this problem, this study created a cleaning module exclusively for printing heads to check whether the durability of printing heads is improved through analysis of printing results before and after using the cleaning module. To this end, this research used a thermal bubble jet printing head, and the used powder was studied using gypsum powder.

• Archives of Metallurgy and Materials
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• 제63권3호
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• pp.1513-1516
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• 2018

We fabricated two different kinds of composite materials for absorbing microwave in a frequency range of 2 to 18 GHz using coaxial airline and thru-reflect-line (TRL) method. The composite materials having carbon nanotube (CNT) with carbonyl iron (CI) or iron oxide (Fe₃O₄) were fabricated by mixing each components. Magnetic properties were measured by SQUID equipment. Complex permittivity and complex permeability were also obtained by measuring S-parameters of the toroidal specimen dispersing CI/CNT and Fe₃O₄/CNT into the 50 weight percent (wt%) epoxy resin. The real permittivity was improved by mixing the CNT however, the real permeability was same as pure magnetic powders. The CI/CNT had a maximum value of real permittivity and real permeability, 11 and 1.4 at 10 GHz, respectively. The CNT composites can be adapted to the radar absorbing materials, band width 8-12 GHz.

• 한국산학기술학회논문지
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• 제17권4호
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• pp.772-779
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• 2016

수용액에서 질산 은과 Trisodium Citrate(TSC)을 반응시켜 은 나노입자를 제조하였다. 은 나노입자의 크기와 모양은 주사 전자 현미경(SEM)을 사용하여 조사하였다. 은 나노입자의 합성실험은 질산 은 수용액의 농도, TSC의 첨가량, 용제, 계면활성제, 초음파 파쇄, 분산제를 변수로 하여 수행하였다. 질산 은의 농도를 높이거나 TSC의 농도를 증가시킬수록 입자의 크기가 커지거나 응집되는 결과를 확인할 수 있었다. 주사 전자 현미경(SEM) 분석 자료로부터 합성된 은 나노입자는 좁은 영역의 입자 크기 분포를 가진 구형 또는 구형에 가까운 것을 확인하였다. 용제를 첨가하여 분산을 시도하였는데, 소수성 용제는 분산성에 영향을 미치지 않았고 친수성 용제는 분산성을 향상시켜 주었다. 계면활성제(HPMC)를 첨가하면 은 나노입자의 크기가 50-100 nm로 커지며, 모양은 불균일하고 부분적인 응집이 발생하였다. 은 나노입자의 분산성은 분산제 첨가 후에 3 시간 이상의 초음파 파쇄에 의해 크게 향상되었다. 분산제의 첨가에 의해 완전한 분산이 일어났으며, 은 나노입자의 크기는 BYK-182(30-40 nm) < BYK-192(42-78 nm) < BYK-142 (51-113 nm)순으로 나타났다. 0.002 M 질산 은 용액에 2-4wt%의 TSC를 첨가하였을 때 38.45-46.28 nm의 은 나노입자가 합성되었다.

• 사상체질의학회지
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• 제13권1호
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• pp.8-16
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• 2001

We analyzed 57 types of herbal medicines for Soeumin, clinically applied in Dongyisoosebowon. In order co discover the standard of herbal classification for the Sasang Constitutions, four concepts of Sasang Medicine were applied. These included 'Sadangron (theory of four groups)', 'Seungganggaehap(ascending-descending and gathering-dispersing)', 'Pyorihanyoul(exterior-interior and hot-cold)', and 'Hyungchiaekmi(fragrance, smell, bodily fluid and taste)'. According to these analyzing methods of herbal properties, we have reached the following conclusions: 1. Lee Je-ma first established the physiology of the internal organs of the Sasang Constitutions through the understanding of constitutional pathology. Dr. Lee then classified herbal medicines into four constitutional groups by observing the herbal effects according to such perspective of organ physiology and pathology. 2. Among the Sasang concepts applied in the analysis of herbal properties based on the physiology and pathology of Sasang constitutions, 'Seungganggaehap (ascending-descending and gathering-dispersing)' was found to be the most useful. Meanwhile, 'Sadangron, (the theory of four groups - Spirit, Qi, Blood and Essence),' along with 'Pyorihanyoul (exterior-interior and hot-cold)' and 'Hyungchiaekmi (fragrance, smell, bodily fluid and taste)' were partially useful. 3. Herbal medicines for Soeumin are characterized by ascending energetics that protect the Yang Qi. The 'Exterior heat disease' is treated with herbal medicines that raise the "Exterior Yang" in three different way: by tonifying Qi. by tonifying Blood and by releasing exterior. The 'Interior cold disease' is treated with herbal medicines that descend "Interior Yin" in two ways. One by warming the stomach, and the other by regulating Qi. 4. Cases where a whole category of herbs with the same effect have been applied co one constitution, are most frequent among Shaoyin herbs. There was an intimate connection between the treatment methods and the traditional effects of herbs for 'Soewnin'. These discoveries allowed us to see that the development of the pharmacology of the Sasang Constitutional pathology more progressed in 'Soeumin'. *analysing simple herbs of "DongEuiBoGam JangBu" we compare JangBu of traditional oriental medicine with JangBu of Sasang Constitutional Medicine. So we can comprehend the JangBu's difference of traditional-oriental with sasang-constitional medicine.

• 한국구조물진단유지관리공학회 논문집
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• 제15권1호
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• pp.159-168
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• 2011

본 연구에서는 분산제 코팅을 통해 성능 개선된(EP) 나일론 섬유를 혼입한 자기충전 콘크리트의 가능성을 알아보고자 하였으며, 이를 위한 실험 방법으로 나일론 섬유 길이와 다른 유기계 섬유(폴리프로필렌, 셀룰로오스)를 혼입한 경우 그리고 광물질 혼화재(고로슬래그 미분말, 플라이애쉬)의 종류를 달리 혼합한 2성분계 및 3성분계의 경우를 가지고 자기충전 콘크리트의 특성을 검토하였다. 이 실험 결과를 토대로 하여 실구조물 적용을 위한 Mock-up Test를 성능 개선된 나일론 섬유를 혼입한 자기충전콘크리트 와 일반콘크리트를 비교하여 실구조물 활용 가능성을 검토 하였다. 그 결과 굳지 않은 자기충전 콘크리트의 특성, 경화된 자기충전 콘크리트의 특성 및 내구특성을 종합해 볼 때 성능 개선된(EP) 나일론 섬유가 우수함을 알 수 있었고, 성능 개선된 나일론 섬유에 따른 광물질 혼화재 사용에서는 플라이애쉬 보다 고로슬래그 미분말이 우수함을 알 수 있었다.

• Transactions on Electrical and Electronic Materials
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• 제16권2호
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• pp.53-61
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• 2015

High-energy ball milling was tested as a method for producing Ultra High Molecular Weight Polyethylene (UHMWPE)- based nanodielectrics containing 1 wt% and 5 wt% OctaIsoButylPOSS (OibPOSS). Qualitative and quantitative evaluations were used to explore the compatibility between OibPOSS and PE. Several ball milling variables were optimized in a bid to achieve UHMWPE/OibPOSS nanodielectrics. The morphology, as well as the thermal and the dielectric properties of the samples, were characterized by scanning electron microscopy, thermogravimetric analysis, broadband dielectric spectroscopy, and progressive-stress breakdown tests. The results showed that (i) ball milling was an effective method for producing UHMWPE/OibPOSS dielectric composites, but appeared ineffective in dispersing OibPOSS at the nanoscale, and (ii) the resulting UHMWPE/OibPOSS dielectric composites presented thermal and dielectric properties similar to those of neat UHMWPE.

• 천문학회보
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• 제40권1호
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• pp.58.3-59
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• 2015

Dynamical expansion of H II regions plays a key role in dispersing surrounding gas and therefore in limiting the efficiency of star formation in molecular clouds. We use analytic methods and numerical simulations to explore expansions of spherical dusty H II regions, taking into account the effects of direct radiation pressure, gas pressure, and total gravity of the gas and stars. Simulations show that the structure of the ionized zone closely follows Draine (2011)'s static equilibrium model in which radiation pressure acting on gas and dust grains balances the gas pressure gradient. Strong radiation pressure creates a central cavity and a compressed shell at the ionized boundary. We analytically solve for the temporal evolution of a thin shell, finding a good agreement with the numerical experiments. We estimate the minimum star formation efficiency required for a cloud of given mass and size to be destroyed by an HII region expansion. We find that typical giant molecular clouds in the Milky Way can be destroyed by the gas-pressure driven expansion of an H II region, requiring an efficiency of less than a few percent. On the other hand, more dense cluster-forming clouds in starburst environments can be destroyed by the radiation pressure driven expansion, with an efficiency of more than ~30 percent that increases with the mean surface density, independent of the total (gas+stars) mass. The time scale of the expansion is always smaller than the dynamical time scale of the cloud, suggesting that H II regions are likely to be a dominant feedback process in protoclusters before supernova explosions occurs.

• 한국태양에너지학회 논문집
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• 제32권6호
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• pp.85-92
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• 2012

A nanofluid is a fluid containing suspended solid particles, with sizes on the order of nanometers. Normally, nanofluids have higher thermal conductivitiest han their base fluids. Therefore, we measured the thermal conductivity and viscosity of oxidized carbon nanofluids based the mixture of distilled water and ethanol (ethanol concentration is 0.2) oxidized carbon nanofluids were made by ultrasonic dispersing oxidized multi-walled carbon nanotubes in the mixture of distilled water and ethanol at the rates of 0.001~ 0.1 vol%. The thermal conductivity and viscosity of oxidized carbon nanofluids were measured by using transient hot-wire method and rotational digital viscometer, respectively. And all of experiments were carried out at the same temperature conditions($10^{\circ}C$, $25^{\circ}C$ and $70^{\circ}C$). As a result, when volume fraction of nanofluids is 0.1 vol%, thermal conductivity was improved 13.6% ($10^{\circ}C$), 15.1% ($25^{\circ}C$), and 17.0% ($70^{\circ}C$), and its viscosity was increased by 36.0% ($10^{\circ}C$), 32.9% ($25^{\circ}C$) and 19.5% ($70^{\circ}C$) than the base fluids.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.26.1-26.1
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• 2009

A simple route of external mechanical force is presented for enhancing the electrical properties of polymer nanocomposite consisted of nanowires. By dispersing ZnO nanowires in polymer solution and drop casting on substrates, nanocomposite transistors containing ZnO nanowires are successfully fabricated. Even though the ZnO nanowires density is properly controlled for device fabrication, as-cast device doesn't show any detectable currents, because nanowires are separated far from each other with the insulating polymer matrix intervening between them. Compared to the device pressed at 300 kPa, the device pressed at 600 kPa currents increased by 50times showing the linear behavior against drain voltage and exhibits promising electrical properties, which operates in the depletion mode with higher mobility and on-current. Such an improved device performance would be realized by the contacts improvement and the increase of the number of electrical path induced by external force. This approach provides a viable solution for serious contact resistance problem of nanocomposite materials and promises for future manufacturing of high-performance devices.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.26.2-26.2
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• 2009

A simple route of externalmechanical force is presented for enhancing the electrical properties ofpolymer nanocomposite consisted of nanowires. By dispersing ZnO nanowires inpolymer solution and drop casting on substrates, nanocomposite transistorscontaining ZnO nanowires are successfully fabricated. Even though the ZnOnanowires density is properly controlled for device fabrication, as-cast devicedoesn't show any detectablecurrents, because nanowires are separated far from each other with theinsulating polymer matrix intervening between them. Compared to the devicepressed at 300 kPa, the device pressed at 600 kPa currents increased by 50times showing the linear behavior against drain voltage and exhibits promisingelectrical properties, which operates in the depletion mode with highermobility and on-current. Such an improved device performance would be realizedby the contacts improvement and the increase of the number of electrical pathinduced by external force. This approach provides a viable solution for seriouscontact resistance problem of nanocomposite materials and promises for futuremanufacturing of high-performance devices.