• 전자공학회논문지CI
• /
• 제43권2호
• /
• pp.72-80
• /
• 2006

본 논문에서는 3차원 모델을 검색하기 위한 형태 기반 기술자를 추출하는 새로운 알고리즘을 제안한다. 제안한 형태 기반 기술자는 모델의 기하학적인 특성을 고려하여 레이 캐스팅 샘플링과 구면조화함수를 이용하는 방법이다. 레이 캐스팅 기법은 모델의 외형을 고려한 적응적인 방법으로 샘플링한다. 이 기법을 통해 기술자에 포함되는 형태 정보를 증가시켜 기술자의 식별성을 높인다. 구면조화함수 계수 추출에서는 기하학적인 주파수 특성을 고려하여 적응적인 계수를 추출한다. 이 방법은 검색 성능에 영향을 미치지 않고 기술자를 조밀하고 간결하게 만든다. 최종적으로 두 방법을 결합함으로서 검색 엔진에서 이용가능하고, 식별성이 향상되며 간결해진 기술자를 생성한다.

• 보존과학회지
• /
• 제28권4호
• /
• pp.417-425
• /
• 2012

청동기시대 청동잔무늬거울은 당대 최고의 합금, 주조기술과 최고 경지의 수공예 세공기술, 조형 수준을 보여주는 것으로, 이번에 시도된 국보 제141호와 제143호 청동잔무늬거울의 복원 제작기술에는 밀랍주조법과 주물사주조법을 사용하였다. 또한 복원된 청동잔무늬거울을 대상으로 주성분분석, 미세조직, X-ray 촬영, SEM-EDS 분석을 실시하였다. 주물사주조법으로 주조한 청동거울은 내부의 공석상은 거의 존재하지 않는 ${\alpha}$ 수지상조직만이 관찰되며, 밀랍주조법의 경우는 ${\alpha}$ 수지상 사이로 공석상이 존재함을 확인할 수 있다. 복원 청동거울 분석을 통한 밀랍주조법과 주물사주조법을 상호 비교해 보면 대체로 주물사주조법이 밀랍주조법에 비하여 주조성이 좋고 냉각속도가 늦어 더 선명하고 균일한 청동거울을 얻을 수 있는 것으로 보인다. 이상과 같이 밀랍주조법과 주물사주조법으로 주조한 청동거울은 서로 큰 차이가 있음을 복원한 청동거울들과 미세조직 분석을 통하여 확인할 수 있었다. 앞으로도 이러한 연구가 계속적으로 진행되어 고대 청동거울들의 제작기법을 다양한 방법으로 규명할 수 있는 기회가 되었으면 한다.

• 소성∙가공
• /
• 제21권3호
• /
• pp.195-201
• /
• 2012

A vacuum ladling die casting system is suggested as a means to obtain a high vacuum level. A high vacuum of 17.8 mmHg is obtained by sealing the inner space of the mould. The sample product is a rear-head housing for an auto-compressor, and the die-casting with 6-cavities was conducted. The flow analysis shows that the filling speed during vacuum ladling is faster than for a non-vacuum system. The air holes in the sample product were too small to be seen with the naked eye in X-ray films. Density tests show that the high vacuum ladling system reduces the internal porosity as much as 57.8% when compared to the non-vacuum system. A defective rate of only 0.17% was found from leak testing. The results of this research prove that the high vacuum die-casting process is useful for manufacturing of aluminium components under high internal pressure.

• 대한치과기공학회지
• /
• 제32권4호
• /
• pp.307-315
• /
• 2010

Purpose: The purpose of this study was to investigate the change of microstructures and mechanical properties of pure titanium casting specimens as a function of mold temperatures. Methods: The pure titanium castings were fabricated using the centrifugal vacuum casting method with different mold temperatures of $200{\sim}500^{\circ}C$. The resulting castings were characterized by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and vicker,s hardness tester. Results: In case of the mold temperatures over $400^{\circ}C$, the porosity, surface crack and large grain size were observed in resulting castings. Conclusion: In this work, The most suitable mold temperature in casting of pure titanium was $300^{\circ}C$.

• 한국주조공학회지
• /
• 제30권1호
• /
• pp.5-13
• /
• 2010

This article aims to introduce the synchrotron radiation for its utilization in the casting and solidification fields as an unique tool for observation of real time phenomena of molten metal during solidification. General features of the synchrotron radiation were briefly introduced for readers in the casting and solidification fields, with no background regarding to synchrotron radiation. And basic principles of imaging technologies using synchrotron light for in-situ observation of molten metal were explained together with exemplary research works, which were reported on the casting and solidification fields in recent years. As a practical guide, real time observation of Al-Si casting alloy was introduced with experimental facilities, image acquisition, and processing together with representative results.

• 대한의용생체공학회:의공학회지
• /
• 제22권4호
• /
• pp.339-347
• /
• 2001

• 한국세라믹학회지
• /
• 제30권10호
• /
• pp.845-851
• /
• 1993

Low firing temperature substrate were synthesized through tape casting and sintering of glass with cordierite composition and then their properties were investigated. Even though the dielectric properties and XRD patterns of substrates, obtained by tape casting and sintering at 900~100$0^{\circ}C$ for various periods, were similar to those of substrates obtained by dry pressing, the sinterability was enhanced. The substrates were thin and the size was 0.6$\times$50$\times$50mm. From the results of dielectric properties, the sinterability and X-ray diffraction pattern, the proper condition for cofiring process with conductor, Cu, was 90$0^{\circ}C$ for 1h. The properties of the substrate are as follows; the dielectric constant was 5.31(at 1MHz), the dissipation factor was 0.0028, the apparent porosity was 0.28% and the main crystalline phase was $\alpha$-cordierite.

• 한국주조공학회지
• /
• 제26권2호
• /
• pp.85-91
• /
• 2006

Inclusions in Ti investment castings are generally known to have detrimental effects on the performance of the castings. However, actual inclusions are infrequent and hard to be located. As a result, it is extremely difficult to obtain sufficient amount of fatigue test specimens of titanium investment castings having inclusions in the gage section. Thus, in-depth research of the adverse influence of inclusions is also hindered. To address this problem, a new casting methodology of specimens containing hard alpha inclusions was developed in this study. To guarantee successful introduction of an inclusion and casting, a carefully designed mold with 8 legs and a special tool were employed. After solidification, castings were cut, and X-ray radiography determined that the inclusions were successfully incorporated into the castings. The castings were further prepared to obtain multiple test specimens and they were fatigue-tested consecutively. Fractography analysis confirmed that fatigue cracks initiated at the hard alpha inclusion. In a nonlinear regression model, the fatigue life can be modeled as an exponential function with a negative exponent of the cross-sectional area of an inclusion. The fatigue life of Ti specimens containing inclusions is inversely proportional to the cross-sectional area of an inclusion.

• 한국컴퓨터그래픽스학회논문지
• /
• 제17권3호
• /
• pp.1-7
• /
• 2011

최근에 GPU 기반의 볼륨 광선 투사법을 가속화하는 기법들이 많이 연구되고 있다. 하지만 이런 기법들은 CPU-GPU간 데이터 전송 시 병목 현상을 야기하고 계층구조를 표현하기 위한 추가적인 GPU 메모리 공간이 필요할 뿐만 아니라 불투명도 전이 함수가 변경되었을 때 실시간에 대응하지 못하는 문제점들이 발생할 수 있다. 본 논문에서는 이러한 문제점들을 해결하기 위해 GPU 기반의 효율적인 빈 공간 도약 기법을 제안한다. 브릭(brick) 안에 포함되는 복셀들의 최대 밀도 값을 하나의 정점에 저장하고 불투명도 전이 함수에 의하여 투명하다고 판별된 정점들을 기하 쉐이더에서 삭제한다. 이 정점들을 랜더링 시간에 기하 쉐이더의 입력 값으로 사용해 투명하지 않은 영역의 바운딩 박스를 만들어 광선이 효과적으로 진행하도록 한다. 생성된 정점들은 렌더링 중에 시점의 변화에 무관하게 사용할 수 있지만 불투명도 전이 함수가 변경되면 투명하지 않은 정점들을 다시 생성해야 한다. 이는 기하 쉐이더를 통해서 GPU 안에서 고속으로 생성되기 때문에 대화식 처리가 가능하다. 제안하는 방법은 기존 광선 투사법의 결과와 동일한 영상을 생성하며 렌더링 속도는 기존의 방법에 비해 최대 10배 이상 향상되었다.

• 대한치과기공학회지
• /
• 제25권1호
• /
• pp.9-20
• /
• 2003

Using a nickel-chrome casting alloy called 'Rexillium V' which is also available as base metal alloy for dental ceramic crown, 4 types of mixtures(A, B, C, D) with old and new metal were prepared for cyclic casting. The results of cyclic casting can be outlined as follows: 1. For Vickers hardness after casting, specimen A and D tended to have lower hardness in the course of cyclic casting, while specimen B and C tended to higher hardness. 2. The results of X-ray diffraction analysis showed that major crystal phase contained nickelchrome compounds and carbide. 3. The observation results of SEM photographs after cyclic casting show that there was a significant tendency to have similar structures among experimental groups. 4. The results of EDX analysis after cyclic casting showed that there were little differences in chemical composition between parent metal and base metal alloy. Although industrial nickel-chrome cast alloy did not show any significant change in material properties even through cyclic casting over several times, it is recommended that more there be more in-depth studies on how to detect any potential corrosion, discoloration and toxication of dental ceramic crown implanted in patient's oral cavity.