• The Journal of Advanced Prosthodontics
• /
• 제9권5호
• /
• pp.358-363
• /
• 2017

PURPOSE. The purpose of this study was to evaluate the reliability of computer-aided replica technique (CART) by calculating its agreement with the replica technique (RT), using statistical agreement analysis. MATERIALS AND METHODS. A prepared metal die and a metal crown were fabricated. The gap between the restoration and abutment was replicated using silicone indicator paste (n = 25). Gap measurements differed in the control (RT) and experimental (CART) groups. In the RT group, the silicone replica was manually sectioned, and the marginal and occlusal gaps were measured using a microscope. In the CART group, the gap was digitized using optical scanning and image superimposition, and the gaps were measured using a software program. The agreement between the measurement techniques was evaluated by using the 95% Bland-Altman limits of agreement and concordance correlation coefficients (CCC). The least acceptable CCC was 0.90. RESULTS. The RT and CART groups showed linear association, with a strong positive correlation in gap measurements, but without significant differences. The 95% limits of agreement between the paired gap measurements were 3.84% and 7.08% of the mean. The lower 95% confidence limits of CCC were 0.9676 and 0.9188 for the marginal and occlusal gap measurements, respectively, and the values were greater than the allowed limit. CONCLUSION. The CART is a reliable digital approach for evaluating the fit accuracy of fixed dental prostheses.

• 마이크로전자및패키징학회지
• /
• 제16권4호
• /
• pp.1-4
• /
• 2009

본 연구에서는 실리콘 웨이퍼에 2중 다이싱 공정의 적용이 리드-온-칩 패키지로 조립되는 반도체 디바이스의 T.C. ($-65^{\circ}C$에서 $150^{\circ}C$까지의 온도변화에 지배되는 신뢰성 실험) 신뢰성에 어떠한 영향을 미치는 지를 보여준다. 기존 싱글 다이싱 공정은 웨이퍼에서 분리된 디바이스의 테두리 부위가 다이싱으로 인해 기계적으로 손상되는 결과를 보였으나, 2중 다이싱 공정은 분리된 디바이스의 테두리 부위가 거의 손상되지 않고 보존되는 것을 확인할 수 있었다. 이는 2중 다이싱의 경우 다이싱 동안 웨이퍼의 전면에 도입된 노치부위가 선택적으로 파손되면서 분리된 디바이스의 테두리 부위를 보호하기 때문으로 해석된다. 온도변화 실험을 통해 2중 다이싱 공정의 도입이 단일 다이싱 공정에 비해 T.C. 신뢰성에서도 대단히 좋은 결과를 보인다는 것을 확인할 수 있었다.

• Journal of Mechanical Science and Technology
• /
• 제20권7호
• /
• pp.1002-1011
• /
• 2006

In this study, we describe the conventional hot pressing (CHP) of layered $Al-B_4C$ composites and their characterization. The matrix alloy Al-5 wt.%Cu was prepared from elemental powder mixtures. The metal and B4C powders were mixed to produce either $Al-Cu-10vol.%B_4C$ or $Al-Cu-30vol.%B_4C$ combinations. Then, these powder mixtures were stacked as layers in the hot pressing die to form a two-layered composite. Hot pressing was carried out under nitrogen atmosphere to produce $30\times40\times5mm$ specimens. Microstructural features and age hardening characteristics of composites were determined by specimens cut longitudinally. The flexural strength of both layered composites and their monolithic counterparts were investigated via three point bending tests. In the case of layered specimens of both $10vol.%B_4C$ and $30vol.%B_4C$ containing layers were loaded for three-point test. The results show that a homogeneous distribution of $B_4C$ particles in the matrix alloy which is free of pores, can be obtained by CHP method. The ageing behavior of the composites was found to be influenced by the reinforced materials, i.e. higher hardness values were reached in 8 hrs for the composites than that for the matrix alloy. Flexural strength test showed that two-layered composites exhibited improved damage tolerance depending on layer arrangement. Microstructural investigation of the fracture surfaces of the bending specimens was performed by means of scanning electron microscope (SEM). While layer with lower reinforcement content exhibited large plastic deformation under loading, the other with higher reinforcement content exhibited less plastic deformation.

• 대한기계학회논문집A
• /
• 제27권10호
• /
• pp.1793-1799
• /
• 2003

An optimal design of a multi-layered plate structure to endure high-velocity impact has been suggested by using size optimization after numerical simulations. The NET2D, a Lagrangian explicit time-integration finite element code for analyzing high-velocity impact, was used to find the parameters for the optimization. Three different materials such as mild steel, aluminum for a multi-layered plate structure and die steel for the pellet, were assumed. In order to consider the effects of strain rate hardening, strain hardening and thermal softening, Johnson-Cook model and Phenomenological Material Model were used as constitutive models for the simulation. It was carried out with several different gaps and thickness of layers to figure out the trend in terms of those parameters' changes under the constraint, which is against complete penetration. Also, the measuring domain has been shrunk with several elements to reduce the analyzing time. The response surface method based on the design of experiments was used as optimization algorithms. The optimized thickness of each layer in which perforation does not occur has been obtained at a constant velocity and a designated total thickness. The result is quite acceptable satisfying both the minimized deformation energy and the weight criteria. Furthermore, a conceptual idea for topology optimization was suggested for the future work.

• 비파괴검사학회지
• /
• 제19권5호
• /
• pp.369-377
• /
• 1999

본 연구는 다중박막(multi-layer) 구조 모델에 대한 초음파신호처리 적용으로 접합경계면의 결함검출에 관한 연구이다. 이를 위해서 먼저 반도체 검사법에 의하여 박리(delamination). 다이 균열(die crack) 기포(void)의 유무를 확인할 수 있었고, 각 접합계면에서의 단위 cm당 결함 오차율을 모집군 25%이하에서 0.003%까지 측정 가능하였다. 또한 초음파 화상처리를 이용하여 결함 판독 프로그램을 위한 각 패키지별 화상을 8단계에서 16단계까지 데이터 베이스화할 수 있었고, 최종 결과 화면에서는 결함정도를 확률로 표현 가능하도록 하였으며 기포의 가능성도 추론해 볼 수 있다. 그리고, 박리검사 프로그램(delamination inspection program)에 의하여 결함의 크기와 결함의 원인을 16단계로 추론하고. S.A.T 장치에 귀환(feedback)시킬 수 있는 매개변수를 찾을 수 있었다. 특히, 반도체 결함추출 알고리즘 개발로 반도체 결함검사자동화의 기틀을 마련하였고, 향후 결함을 세분화하고 다양한 반도체 패키지별로 데이터베이스를 구축한다면, 온라인 상태에서 보다 많은 검사를 수행 할 수 있는 인공지능형 자동검사 시스템 구현이 가능할 수 있도록 하였다.

• 대한치과기공학회지
• /
• 제30권2호
• /
• pp.87-92
• /
• 2008

Purpose: In this study, we tried to compare marginal accuracy when produce ceramic crown using all ceramic materials and existent metal-ceramic system. Material and methods: All-ceramic systems were E-max (Ivoclar/Vivadent, Lichtenstein), Lava(3M, U.S.A.) and Wol-ceram(Teamziereis, Germany). Metal-ceramic system(PFG) was composed of Au-Pt alloy (Metalor, Switzerlandand) and overlying ceramic(D-sign, Ivoclar/Vivadent, Lichtenstein). We fabricated metal master die with upper diameter of 7.95mm, bottom diameter of 9.00mm, height of 5.00mm, and taper of $6^{\circ}$. All ceramic system used 0.5mm thickness ceramic coping, while metalceramic system used 0.3 thickness metal coping. By adding dentin and enamel ceramics on each coping, a crown with a proximal thickness of 1.0 mm and occlusal thickness of 2.0mm was fabricated. Pressure of 2kg was applied for 10 seconds on each crown with static load compressor. Before and after cementation, we measured the marginal gap at 4 points of each crown using optical microscope. The data was analyzed using a Student's t test and repeated-measures of analyses of variance(ANOVA) followed by a Bonferroni test. A p value<0.05 was considered significant. Results: As experiment results, marginal accuracy of wol-ceram and Lava is no good when compared with marginal accuracy of PFG. But marginal accuracy of E.max is good when compared with PFG. This result showed not significant. The marginal accuracy of E.max is good when compared with marginal accuracy of wol-ceram and Lava. Conclusion: The marginal accuracy of E.max is very good when compared with marginal accuracy of another group.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1996년도 하계학술대회 논문집 C
• /
• pp.2004-2006
• /
• 1996

A thermally driven polysilicon micro actuator has been fabricated using surface micromachining techniques. It consists of P-doped polysilicon as a structural layer and TEOS (tetracthylorthosilicate) as a sacrificial layer. The polysilicon was annealed for the relaxation of residual stress which is the main cause to its deformation such as bending and buckling. And the newly developed HF VPE (vapor phase etching) process was also used as an effective release method for the elimination of sacrificial TEOS layer. The thickneas of polysilicon is $2{\mu}m$ and the lengths of active and passive polysilicon cantilevers are $500{\mu}m$ and $260{\mu}m$, respectively. The actuation is incurred by die thermal expansion due to the current flow in the active polysilicon cantilever, which motion is amplified by lever mechanism. The moving distance of polysilicon micro actuator was experimentally conformed as large as $21{\mu}m$ at the input voltage level of 10V and 50Hz square wave. The actuating characteristics are investigated by simulating the phenomena of heat transfer and thermal expansion in the polysilicon layer. The displacement of actuator is analyzed to be proportional to the square of input voltage. These micro actuator technology can be utilized for the fabrication of MEMS (microelectromechanical system) such as micro relay, which requires large displacement or contact force but relatively slow response.

• 한국응용과학기술학회지
• /
• 제29권1호
• /
• pp.13-18
• /
• 2012

금속 주조시 사용되는 탄소이형제를 카본블랙과 점증제 겸 알데하이드 화합물의 경화제로 사용될 수 있는 수용성 고분자인 잔탄검(X-gum), 카르복시메틸셀룰로오스(CMC)을 혼합하여 제조하였다. 이 때 카본블랙의 안정한 분산을 위하여 0.25 wt%의 X-gum 또는 1.0 wt%의 CMC가 적당하였다. 1.0 wt% 보다 낮은 농도의 CMC를 사용했을 경우 카본블랙이 매우 쉽게 층분리되었다. 유리판에 대한 부착력은 경화제와, 구르탈알데하이드 및 사슬연장제인 올리고당의 양에 비례하였으며. X-gum으로 제조된 탄소 이형제는 CMC를 이용해 제조된 것보다 유리에 대한 부착력이 우수하였다. 결과적으로 본 실험의 최적 조건에서 제조된 탄소이형제는 친환경적으로 주조시에 적용할 수 있을 것으로 판단된다.

• Asian-Australasian Journal of Animal Sciences
• /
• 제27권6호
• /
• pp.791-796
• /
• 2014

Cryopreservation of epididymal sperm is an effective technique to preserve genetic materials of domestic cats and wild felids when they unexpectedly die. However, this technique inevitably causes detrimental changes of cryopreserved-thawed spermatozoa, for example, by physical damage and excessive oxidative stress. L-carnitine is an antioxidant that has been used to improve sperm motility in humans and domestic animals. This study aimed to investigate the effects of L-carnitine on cat epididymal sperm quality following cryopreservation and thawing. After routine castration, cauda epididymides were collected from 60 cat testes. The epididymal spermatozoa from 3 cauda epididymides were pooled as 1 replicate. Spermatozoa samples (16 replicates) were examined for spermatozoa quality and then randomly divided into 4 groups: 0 mM L-carnitine (control), 12.5 mM, 25 mM and 50 mM L-carnitine. The sperm aliquots were then equilibrated and conventionally frozen. After thawing, sperm motility, plasma membrane integrity, DNA integrity and acrosome integrity were evaluated. The 25 mM L-carnitine significantly improved sperm motility compared with a control group (p<0.05), although this was not significantly different among other concentrations. In conclusion, supplementation of 25 mM L-carnitine in freezing extender improves cauda epididymal spermatozoa motility. The effects of L-carnitine on the levels of oxidative stress during freezing and thawing remains to be examined.

• Tribology and Lubricants
• /
• 제31권4호
• /
• pp.157-162
• /
• 2015

In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique is applied to tungsten carbide-cobalt (WC-Co) to extend the service life of carbide parts used in press mold. The UNSM technique modifies the structure, reduces the surface roughness, increases the surface hardness, induces the compressive residual stress, and increases the wear resistance of materials by introducing severe plastic deformation. The surface roughness, hardness, and compressive residual stress of WC after UNSM treatment improve by about 42, 10, and 71%, respectively. A wear test under dry conditions is used to assess the effectiveness of the UNSM technique on the friction and wear behavior of WC. The UNSM technique is found to reduce the WC friction coefficient by approximately 21% and enhance the wear resistance by approximately 85%. The improved friction and wear behavior of WC may be mainly attributed to the increased hardness and compressive residual stress. Moreover, the WC specimen is treated by UNSM technique using three different WC, silicon nitride (Si₃N₄) and stainless steel (STS304) balls. The surface treated by WC balls shows the highest hardness when compared with treatment by stainless steel and silicon nitride balls. According to the obtained results, the UNSM technique is believed to increase the durability of the carbide component by improving the friction and wear behavior.