• 한국기계가공학회지
• /
• 제18권7호
• /
• pp.83-89
• /
• 2019

In the conventional casting and forging method, there is a disadvantage that a mold is an essential addition, and a production cost is increased when a small quantity is produced. In order to overcome this disadvantage, a metal 3D printing production method capable of directly forming a shape without a mold frame is mainly used. In particular, overseas research has been conducted on various materials, one of which is a metal printer. Similarly, domestic companies are also concentrating on the metal printer market. However, In this case of the conventional metal 3D printing method, it is difficult to meet the needs of the industry because of the high cost of materials, equipment and maintenance for product strength and production. To compensate for these weaknesses, printers have been developed that can be manufactured using sand mold, but they are not accessible to the printer company and are expensive to machine. Therefore, it is necessary to supply three-dimensional casting printers capable of metal molding by producing molds instead of conventional metal 3D printing methods. In this study, we intend to reduce the unit price by replacing the printing method used in the sand casting printer with the FDM method. In addition, Ag paste is used to design the output conditions and enable ceramic printing.

• 한국재료학회지
• /
• 제31권1호
• /
• pp.8-15
• /
• 2021

Transparent, photocatalytic, and self-cleaning TiO2 thin film is developed by TiO2 sol-gel coating on glass and polycarbonate (PC) substrates. Acetyl acetone (AcAc) suppresses the precipitation of TiO2 by forming a yellowish (complex) transparent sol-gel. XPS analysis confirms the presence of Ti2p and O1s in the thin films on glass and PC substrates. The TiO2-sol is prepared by stabilizing titanium (IV) isopropoxide (TTIP) with diethylamine and methyl alcohol. The addition of AcAcsilane coupling solution to the TiO2-sol instantaneously turns to yellowish color owing to the complexing of titanium with AcAc. The AcAc solution substantially improves the photocatalytic property of the TiO2 coating layer in MB solutions. The coated TiO2 film exhibits super hydrophilicity without and with light irradiation. The TiO2 thin film stabilized by adding 8.7 wt% AcAc shows the highest photo-degradation for methylene blue (MB) solution under UV light irradiation. Also, the optimum photocatalytic activity is obtained for the 8.7 wt% AcAc-stabilized TiO2 coating layer calcined at 450 ℃. The thin-films on glass exhibit fast self-cleaning from oleic acid contamination within 45 min of UV-light irradiation. The appropriate curing time at 140 ℃ improves the anti-fogging and thermal stability of the TiO2 film coated on PC substrate. The watermark-free PC substrate is particularly beneficial to combat fogging problems of transparent substrates.

• 대한금속재료학회지
• /
• 제48권3호
• /
• pp.194-202
• /
• 2010

Application of a stronger and more durable material for reactor pressure vessels (RPVs) might be an effective way to insure the integrity and increase the efficiency of nuclear power plants. A series of research projects to apply the SA508 Gr.4 steel in ASME code to RPVs are in progress because of its excellent strength and durability compared to commercial RPV steel (SA508 Gr.3 steel). In this study, the microstructural characteristics and mechanical properties of SA508 Gr.3 Mn-Mo-Ni low alloy steel and SA508 Gr.4N Ni-Mo-Cr low alloy steel were investigated. The differences in the stable phases between these two low alloy steels were evaluated by means of a thermodynamic calculation using ThermoCalc. They were then compared to microstructural features and correlated with mechanical properties. Mn-Mo-Ni low alloy steel shows the upper bainite structure that has coarse cementite in the lath boundaries. However, Ni-Mo-Cr low alloy steel shows the mixture of lower bainite and tempered martensite structure that homogeneously precipitates the small carbides such as $M_{23}C_6$ and $M_7C_3$ due to an increase of hardenability and Cr addition. In the mechanical properties, Ni-Mo-Cr low alloy steel has higher strength and toughness than Mn-Mo-Ni low alloy steel. Ni and Cr additions increase the strength by solid solution hardening. In addition, microstructural changes from upper bainite to tempered martensite improve the strength of the low alloy steel by grain refining effect, and the changes in the precipitation behavior by Cr addition improve the ductile-brittle transition behavior along with a toughening effect of Ni addition.

• 한국컴퓨터정보학회논문지
• /
• 제26권3호
• /
• pp.59-67
• /
• 2021

블록체인 기술은 2008년 나카모토 사토시라는 신원미상의 인물이 비트코인이라는 암호화폐를 제안하면서 시작되었다. 나카모토 사토시는 기존의 금융 시스템에 대한 불신을 가지고 있었고 은행과 같은 중개자 없이도 해킹이나 변조에 견고한 금융시스템을 블록체인 기술을 통해 구현하고자 했다. 사토시는 비트코인의 생성과, 거래의 위조를 방지하기 위한 기술로 블록체인을 제안하였고 이를 통해 화폐의 발행과 거래, 그리고 검증의 기능을 구현하였다. 이후 스마트 계약을 블록체인 상에서 구현할 수 있는 암호화폐인 이더리움이 개발되면서 예금, 대출, 보험, 파생상품 등 복잡한 계약이 필요한 금융상품을 암호화폐의 영역으로 끌어들일 수 있게 되었다. 또한 실물자산과 결합을 통해 금융 기관이 제공했던 상품을 대체할 수 있는 가능성도 확대해 나가고 있다. 이러한 애플리케이션들을 Decentralized Finance(DeFi)라고 정의한다. 본 논문은 전반적인 DeFi의 기술적 이해와 현재 운영되고 있는 어플리케이션의 소개를 위하여 작성되었다. 먼저 전반적인 DeFi를 구현하는 기술들과 생태계에 대해서 설명한 후 대표적인 DeFi 애플리케이션들을 특징별로 분류하여 설명한다.

• 대한족부족관절학회지
• /
• 제26권2호
• /
• pp.84-87
• /
• 2022

Purpose: This was a pilot study to examine the clinical usefulness of the newly developed three-dimensional sweep mode extracorporeal shockwave treatment (ESWT) in patients with plantar fasciitis. Materials and Methods: Three-dimensional sweep mode ESWT was performed once a week for 5 weeks in patients with plantar fasciitis who showed no improvement with the conventional conservative treatment. A 100-mm visual analogue scale (VAS) reading for pain from walking and at rest after walking were collected before the treatment and 8 and 16 weeks after the initial treatment. In addition, the Foot and Ankle Outcome Score (FAOS) and EuroQol-5-dimension (EQ-5D) scores before and 16 weeks after the treatment were evaluated. Results: VAS for pain for walking improved from 50.60±8.38 to 19.80±15.61 at 8 weeks after the initial treatment (p=0.008) and 9.80±9.62 at 16 weeks after the treatment (p<0.001). VAS for pain at rest after walking improved from 36.60±19.55 to 11.80±12.95 at 8 weeks after the initial treatment (p=0.052) and 8.80±8.87 at 16 weeks after the treatment (p=0.024). Preoperative FAOS increased from an average of 74.80±9.73 before the treatment to an average of 81.00±8.86 at week 16 after the procedure (p=0.49) and compared to pre-treatment levels, there was a decrease of one level in the anxiety/depression domain of the EQ-5D, post-treatment. Conclusion: The results of this preliminary study confirmed that the newly developed EWST with the smart forging sweep mode was effective in improving pain and function in plantar fasciitis.

• 박물관보존과학
• /
• 제28권
• /
• pp.65-88
• /
• 2022

탄환의 특성과 거동은 화기 성능과 직결되므로 매우 중요하다. 그러나 전통 탄환과 관련된 연구 성과는 사실상 적은 편이다. 본고에서는 육군박물관 소장 조선시대 금속제 탄환의 재료와 제작 공정을 알아보기 위해 과학적 분석을 실시했다. 또한 탄환 직경에 따라 사용 가능한 조선시대 화기 종류를 분류하여 정리했다. 그 결과 탄환은 철환, 납환 및 수철연의환으로 구분되었다. 대부분의 철환과 납환은 주조로 제작되었다. 일부 철환은 단조로 제작되었다. 수철연의환은 철환을 주형에 넣은 후 용융된 납을 부어 주조하여 제작된 것으로 추정된다. 한편 탄환은 재료에 따라 비중이 확연히 구분되는 것을 확인할 수 있었다. 마지막으로 조사 대상 탄환은 소형 총통, 조총, 불랑기포, 현자총통, 대위원포, 소포, 홍이포 등에 사용 가능했다.

• 수완나부미
• /
• 제6권2호
• /
• pp.3-18
• /
• 2014

With natural resources-terrestrial or coastal-fastly diminishing, governments are now resorting to biodiversity conservation, fast-tracking the introduction of new legislations, as well as the amendment of existing ones, and laying out programs that interpret existing practices and research agendas. This paper examines how biodiversity conservation-in addition to eco-tourism-has become an important symbol of the modernizing state of Sabah, Malaysia. It further examines the effects of biodiversity conservation on state and community management of natural resources, with particular reference to the management of natural resources by the indigenous peoples of Sabah. Citing case studies and focusing on a forest community at Kiau Nuluh, in the district of Kota Belud, Sabah, this paper evaluates strategies used by indigenous groups to maintain access and control over the management of natural resources-and by implication to livelihoods-via ecotourism, making creative alliances with non-government organisations as well as forging cooperation with government agencies which act as custodians of these resources. For a majority of indigenous groups however, the practice of biodiversity conservation has meant reduced and controlled access to natural resources, considering the fundamental issue of the lack of security of tenure to the land claimed under customary rights. New initiatives at recognizing Indigenous and Community Conserved Areas (ICCAs) by international conservation groups provide a means for tenure recognition, for a price, of course. The recognition of ICCAs also faces obstacles arising from developmentalist ideology which upholds that forests are valuable only when converted to other land use, and not left to stand for their intrinsic value.

• 한국재료학회지
• /
• 제33권12호
• /
• pp.558-564
• /
• 2023

In this study, we designed and manufactured a large angular contact ball bearing (LACBB) with low deformation using JIS-SUJ2 steel and analyzed changes in its structural characteristics and chemical composition upon heat treatment. The bearing was produced by hot forging and heat treatment including a quenching and tempering (Q/T) process, and its properties were analyzed using 4 mm thick specimens. A difference in the size distribution of the carbide in the outer and inner parts of the bearing was observed and it was confirmed that large and non-uniform carbide was distributed in the inner part of the bearing. After heat treatment, the hardness value of the outer part increased from 13.4 HRC to 61 HRC and the inner part increased from 8.0 HRC to 59.7 HRC. As a result of X-ray diffraction (XRD) measurements, the volume fraction of the retained austenite contained in the outer part was calculated to be 3.5~4.8 % and the inner part was calculated to be 3.6~5.0 %. The surface chemical composition and the content of chemical bonds were quantified through X-ray photoelectron spectroscopy (XPS), and a decrease in C=C bonds and an increase in Fe-C bonds were confirmed.

• 한국분말재료학회지
• /
• 제31권1호
• /
• pp.50-56
• /
• 2024

We report the effect of plastic deformation on the thermoelectric properties of n-type Bi₂Te_2.5Se_0.5 compounds. N-type Bi₂Te_2.5Se_0.5 powders are synthesized by an oxide-reduction process and consolidated via spark-plasma sintering. To explore the effect of plastic deformation on the thermoelectric properties, the sintered bodies are subjected to uniaxial pressure to induce a controlled amount of compressive strains (-0.2, -0.3, and -0.4). The shaping temperature is set using a thermochemical analyzer, and the plastic deformation effect is assessed without altering the material composition through differential scanning calorimetry. This strategy is crucial because the conventional hot-forging process can often lead to alterations in material composition due to the high volatility of chalcogen elements. With increasing compressive strain, the (00l) planes become aligned in the direction perpendicular to the pressure axis. Furthermore, an increase in the carrier concentration is observed upon compressive plastic deformation, i.e., the donor-like effect of the plastic deformation in n-type Bi₂Te_2.5Se_0.5 compounds. Owing to the increased electrical conductivity through the preferred orientation and the donor-like effect, an improved ZT is achieved in n-type Bi₂Te_2.5Se_0.5 through the compressive-forming process.

• 헤리티지:역사와 과학
• /
• 제49권2호
• /
• pp.172-189
• /
• 2016

본 연구에서는 "오주서종박물고변(五洲書種博物考辯)", "천공개물(天工開物)" 등 고문헌에 기록된 오동 재료와 합금비, 주조 시설, 주조법 등을 확인하고 이를 기초자료로 활용하여 오동상감기법으로 장도를 제작하였다. 오동상감기법 장도 제작은 크게 오동 합금, 은땜 합금, 오동판과 은판 제작, 칼자루와 칼집 제작, 장도의 장석인 두겁 및 부속품 제작, 오동 상감, 조립의 순으로 진행하였다. 오동의 합금은 "오주서종박물고변"에 보이는 상품(上品)으로 전통방식의 진오동(眞烏銅) 합금비인 구리와 금을 20:1의 중량비로 하였다. 은땜의 합금은 상감된 문양에 사용한 경우 은과 황동(Cu 7 : Zn 3)을 중량비 5:1로, 단순 접합 사용한 경우에는 은과 황동을 중량비 5:2로 합금하여 은땜판을 제작하였다. 칼집과 칼자루 제작은 진오동 합금비로 만든 오동 괴를 풀림과 단조작업을 실시하여 오동판의 두께를 0.6mm로, 오동의 뒷면인 은판도 두께 0.6mm로 제작한 뒤, 오동판과 은판 접합, 풀림과 단조, 오동판에 문양 새기기, 은 상감하기, 오동판으로 칼집과 칼자루 모양잡기, 은땜으로 접합하기, 연마 및 광택내기 등의 과정을 거쳐 완성하였다. 붉은색의 오동판 표면을 검은색으로 부식시키는 '오동 살리기(발색하기)'는 오동 합금의 품위에 따라 발색 효과가 차이가 난다. 한지를 30일 정도 썩힌 인뇨(人尿)에 적셔 칼집과 칼자루 등에 감아 따뜻한 곳($25^{\circ}C$ 이상)에 두고 2~3시간이 경과하면 오동판의 겉면만 검은색으로 발색되고 은이 상감된 문양은 그대로 있어 오동상감기법을 재현할 수 있었다. 오동상감 복원에 사용했던 오동판, 은판, 은땜판의 합금성분과 오동의 표면 발색성분을 알기 위해 과학분석을 실시하였다. 오동 합금 분석(시료 2개)결과 고문헌 기록(Cu 95wt%, Au 5wt%)과 평균성분비가 유사한 Cu 95.57wt%, Au 4.16wt%과 차이가 있는 Cu 98.04wt%, Au 1.95wt%로 검출되었는데, 전자는 오동판 가공에 성공률이 높은 반면, 후자는 가공과정에서 터지는 등의 실패가 있었다. 오동판과 은판이 부착된 시료의 성분분석 결과 은판 부분은 Ag 100wt%로 검출되었고, 오동판과 은판이 접합된 부분은 Cu, Ag, Au가 모두 검출되어 접합이 잘 되었음을 확인할 수 있었다. 은과 황동을 합금한 은땜판은 분석결과 Ag 성분이 다양하게 검출되고 있어 성분비와 관계없이 매우 불균질하게 섞여있음을 관찰하였다. 오동판에 검은색으로 발색된 부분의 성분분석 결과 소지 금속에서 검출되지 않았던 S의 함량이 검출되어 S의 함량이 오동 색상에 영향을 미친 것으로 판단되었다. 향후 발색에 대한 정확한 메커니즘을 밝히기 위해서는 추가적인 화합물, 색도 및 재현 연구 등 추가연구가 필요하다. 이번 연구를 통해 시도 및 확인된 고문헌 속의 오동합금 실험 및 재현, 오동상감기법에 의한 장도제작, 오동판 검은색 발색 메커니즘의 과학 분석결과 등은 오동상감기법의 복원을 위한 중요한 기초자료로 활용될 수 있을 것이다.