• 생물환경조절학회지
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• 제6권3호
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• pp.159-167
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• 1997

플러그육묘의 대량생산 보급에 대처하기 위하여는 정식기의 보급이 필요하다. 본 연구에 서는 국내보급중인 반자동정식기의 정식성능을 조사 분석하므로써 기계정식 작업시 최적작업조건 구명과 정식기 연구 개발의 기초 자료를 획득하고자 실시하였고, 정식시험을 실시한 결과를 요약하면 다음과 같다. 1. 호퍼의 크기는 정식자세와 정식율에 영향을 미치고, 진압이 불량한 정식육묘는 1일후 고사하므로 재관수가 필요하였다. 따라서 복토진압장치는 전후좌우 진압법이 좋으며, 2중관수장치에 의하여 정식시의 관수량을 늘려야할 것으로 생각되나 물통의 용량이 또한 커지게 되어 기계의 운전 조작이 어렵게 되므로 자동육묘공급 정식기는 공간문제와 1~2인 작업을 전제로 할 때 효율면에서 자동관수는 없는 것이 바람직할 것으로 사료된다. 2. 반자동정식기는 몇 가지의 구조적 개선이 필요하지만 현재로도 정식기계의 운전을 주행 속도 14m/min 이하, 정식깊이 2~3cm, 간격 30cm로 하고 고추 육묘는 128공의 45일 육묘, 배추는 128공의 25육묘를 사용하면 플러그육묘의 정식에 적합한 것으로 생각된다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 춘계학술대회 논문집
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• pp.23-28
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• 2002

This paper describes the machining characteristics of the $MoSi_2$ based composites by electric discharge drilling with various tubular electrodes, besides, Hardness characteristics and microstructures of $Nb/MoSi_2$ laminate composites were evaluated from the variation of fabricating conditions such as preparation temperature, applied pressure and pressure holding time. $MoSi_2$ -based composites has been developed in new materials for jet engine of supersonic-speed airplanes and gas turbine for high- temperature generator. Achieving this objective may require new hard materials with high strength and high temperature-resistance. However, With the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material, the tool electrode being almost non-unloaded, because there is no direct contact between the tool electrode and the workpiece. By combining a nonconducting ceramics with more conducting ceramic it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and $MoSi_2$ powder was an excellent strategy to improve hardness characteristics of monolithic $MoSi_2$. However, interfacial reaction products like (Nb, Mo)$SiO_2$ and $Nb_2Si_3$ formed at the interface of $Nb/MoSi_2$ and increased with fabricating temperature. $MoSi_2$ composites which a hole drilling was not possible by the conventional machining process, enhanced the capacity of ED-drilling by adding $NbSi_2$ relative to that of SiC or $ZrO_2$ reinforcements.

• 한국산학기술학회논문지
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• 제16권3호
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• pp.1645-1651
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• 2015

본 연구에서는 선삭 작업에서 가공 여유각 변경에 따른 피삭재의 형상정밀도가 어떻게 변화되는지 분석하고자 하였다. 피삭재는 3가지로 SM45C(기계구조용탄소강), SCM415(크롬몰리브덴강), STS303(스테인리스강)을 선택하여 정해진 가공조건인 회전속도 2,500 rpm으로 시작하여 이송속도 0.07 mm/rev와 0.10 mm/rev를 기준으로 가공깊이 0.1 mm, 0.2 mm, 0.3 mm 그리고, 절인 경사각인 네거티브 경사각 $0.0^{\circ}(-6.0^{\circ})$, $0.3^{\circ}(-6.3^{\circ})$, $0.9^{\circ}(-6.9^{\circ})$의 3가지 형태로 가공하였을 경우, 재료별 가공정밀도, 원통도, 동축도, 진원도 등의 결과를 비교 분석하였다. 피삭재의 재질별로 알아본 원통도의 정밀도는 $0.0^{\circ}{\rightarrow}0.3^{\circ}{\rightarrow}0.9^{\circ}$의 순으로 $0.9^{\circ}$일 경우가 가장 좋은 원통도 값을 나타냈다. 결과적으로 바이트의 네거티브 경사각이 커지면 정밀도가 특정 부분에서 재질에 관계없이 좋아져서 가공성이 향상됨을 알 수 있었다. 또한, 이송속도와 절삭 깊이에 따라 가공형상이 변화한다는 것과 재질에 따라 다르게 적용되어야 한다는 것을 확인하게 되었다.

• 한국통신학회논문지
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• 제37B권9호
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• pp.806-813
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• 2012

클라우드 컴퓨팅 환경에서 Infrastructure as a Services (IaaS), Platform as a Services (PaaS), Software as a Services (SaaS), Desktop as a Services (DaaS) 등 다양한 솔루션들이 지속적으로 제공되고 있다. 현재는 사용자 단말이 클라우드 서비스를 제공받으면서 이동성을 보장하기 위한 솔루션으로 Mobile as a Services(MaaS)가 가장 많은 주목을 받고 있다. 사용자는 이동을 하면서도 클라우드에 있는 데이터 및 어플리케이션에 대한 접근과 이용이 가능해야 한다. 다시 말해 모바일 Thin-Client 환경에서 클라우드와 통신, 이동성 지원은 필수 요소이다. 모바일 단말의 이동성을 지원하기 위해 MobileIPv6 (MIPv6) 및 Proxy Mobile IPv6 (PMIPv6)가 소개되면서 많은 연구가 진행되고 있다. 또한, PMIPv6에 대한 연구는 도메인 내에 패킷 손실을 우려한 최적 경로 설정, 빠른 핸드 오버 등의 개선방안이 많이 제시된 바 있다. 본 논문은 모바일 Thin-Client 지원을 위해 PMIPv6 및 클라우드 연동 시스템을 제안한다. 제안한 시스템에서 모바일 Thin-Client가 서비스를 지원받기 위해 Replica서버를 이용하여 원활한 서비스를 제공하는 기법을 제안하며 성능평가를 통하여 기존 PMIPv6에서 핸드오버에 대한 데이터 비용을 비교 분석할 것이다.

• 한국수자원학회논문집
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• 제53권4호
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• pp.273-283
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• 2020

지하수자원의 변동성 및 취약성 평가를 위한 지하수위의 정량적 예측은 매우 중요하다. 이를 위해 다양한 시계열 분석 기법과 머신러닝 기법 등이 사용되어 왔다. 본 연구에서는 제주도 한경면 지역에 설치된 11개 지하수위 관측정의 일 수위자료를 대상으로 인공신경망 알고리즘의 하나인 Long short term memory (LSTM)에 기반한 예측 모델을 개발하였다. 제주도의 지하수위는 일반적으로 조석에 의한 자기상관성이 높고 강수에 의한 영향이 잘 반영되는 것으로 알려져 있다. 이러한 자료 특성을 고려한 입출력 텐서를 구성하기 위해 각 지하수 관측정의 수위변동 관측 자료와 같은 기간의 강수량 자료를 추가 입력자료로 선택하였다. 4계절을 나타내는 초기 365일 자료를 이용하여 LSTM 모델을 학습시켰으며 나머지 자료를 검증에 활용하여 예측 모델의 적합도를 평가하였다. 모델의 개발은 Python기반 딥러닝 프레임워크인 Keras를 이용하였고, 학습속도를 향상시키고자 NVIDIA CUDA 아키텍처를 도입하였다. LSTM 모델을 이용하여 지하수위 변화를 학습시키고 검증한 결과 결정계수가 평균 0.98로 나타나 개발된 예측모델의 적합성이 매우 높은 것으로 확인되었다.

• 대한치과교정학회지
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• 제37권5호
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• pp.376-385
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• 2007

고정성 장치를 이용한 교정 치료는 심미적 개선이 주목적 중 하나이나, 금속재 브라켓은 치료기간 동안 비심미적으로 보이는 단점이 있다. 이러한 이유로 치아색과 유사한 심미적 브라켓이 선호되었으나 호선과의 마찰저항이 금속재 브라켓보다 큰 것으로 알려져 있다. 본 연구는 최근 개발된 심미적 브라켓의 일종인 인산칼슘재 브라켓의 마찰저항을 측정하고 기존 금속재 브라켓과 금속슬롯 삽입형 도재 브라켓과의 마찰저항의 차이를 구명(究明)해 보고자 하였다. 실험군으로서 인산칼슘 재질의 Hyaline II (Tomy, Tokyo, Japan) 브라켓을, 대조군으로서 metal slot이 삽입된 도자기 재질인 Clarity (3M Unitek, Monrovia, CA, USA) 브라켓과 스테인레스 스틸 금속재 브라켓인 Kosaka (Tomy, Tokyo, Japan) 브라켓을 사용하고, $0.019\;{\times}\;0.025$ 인치 스테인레스 스틸 강선 (3M Unitek, Monrovia, CA, USA)을 이용하며 결찰재는 합성고무링 (Ormco, Glendora, CA, USA)을 사용하였다. 치아의 생리학적 환경을 재현하기 위해 모의 생물학적 모형을 고안하였으며 이에 강선을 삽입하여 load cell (Push & pull gauge, RX-2 AIKOH, Osaka, Japan)로 분당 5 mm로 견인하며 만능시험기(Instron4467, Instron, Norwood, MA, USA)로 마찰저항을 측정하였다. 실험결과, 실험군인 인산칼슘 재질 브라켓의 마찰저항은 대조군인 금속슬롯 삽입형 도재 브라켓 보다 작고 (p < 0.01) 금속재 브라켓의 마찰저항보다 크게 나타나 (p < 0.05), 인산칼슘재 브라켓은 심미적 측면에서 금속재 브라켓을, 효율적 측면에서 금속슬롯 삽입형 도재 브라켓을 대체하여 사용 가능함을 시사하였다.

• The Journal of Advanced Prosthodontics
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• 제7권1호
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• pp.1-7
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• 2015

PURPOSE. This study was performed to evaluate shear bond strength (SBS) between three dual-cured resin cements and silica coated zirconia, before and after thermocycling treatment. MATERIALS AND METHODS. Sixty specimens were cut in $15{\times}2.75mm$ discs using zirconia. After air blasting of $50{\mu}m$ alumina, samples were prepared by tribochemical silica coating with $Rocatec^{TM}$ plus. The specimens were divided into three groups according to the dual-cure resin cement used: (1) Calibra silane+$Calibra^{(R)}$, (2) Monobond S+$Multilink^{(R)}$ N and (3) ESPN sil+$RelyX^{TM}$ Unicem Clicker. After the resin cement was bonded to the zirconia using a Teflon mold, photopolymerization was carried out. Only 10 specimens in each group were thermocycled 6,000 times. Depending on thermocycling treatment, each group was divided into two subgroups (n=10) and SBS was measured by applying force at the speed of 1 mm/min using a universal testing machine. To find out the differences in SBS according to the types of cements and thermocycling using the SPSS, two-way ANOVA was conducted and post-hoc analysis was performed by Turkey's test. RESULTS. In non-thermal aged groups, SBS of Multilink group (M1) was higher than that of Calibra (C1) and Unicem (U1) group (P<.05). Moreover, even after thermocycling treatment, SBS of Multilink group (M2) was higher than the other groups (C2 and U2). All three cements showed lower SBS after the thermocycling than before the treatments. But Multilink and Unicem had a significant difference (P<.05). CONCLUSION. In this experiment, Multilink showed the highest SBS before and after thermocycling. Also, bond strengths of all three cements decreased after thermocycling.

• 대한치과보철학회지
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• 제45권4호
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• pp.419-430
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• 2007

Purpose: This in vitro study evaluated shear bond strengths of surface treatment porcelains with four porcelain repair systems simulating intraoral bonding of composite resin to feldspathic porcelain or pressable porcelain. Material and methods: Eighty Porcelain disks were prepared. Group A: forty disk specimens were fabricated with Feldspathic Porcelain($Omega^{(R)}900$, Vident, Menlo Park, CA, USA). Group B: forty disk specimens were fabricated with Pressable Porcelain(IPS Empress 2 ingot, Ivoclar-Vivadent, Schaan, Liechtenstein, Germany). Each groups was divided into 4 subgroups and composite resin cylinders were bonded to specimen with one of the following four systems: Clearfil Porcelain Bond(L. Morita, Tustin, CA, USA), Ulradent Porcelain Etch. (Ultradent, Salt Lake City UT, USA), Porcelain Liner-M(Sun Medical Co., Kyoto, Japan), Cimara Kit(Voco, Germany). After surface conditioning with one of the four porcelain repair systems substrate surfaces of the specimen were examined microscopically(SEM). Shear bond strengths of specimens for each subgroup were determined with a universal testing machine (5mm/min crosshead speed) after storing them in distilled water at $37{\pm}1^{\circ}C$ for 24 hours. Stress at failure was measured in $MP_a$, and mode of failure was recorded. Differences among four repair systems were analyzed with two way ANOVA and Duncan test at the 95% significance level. Results: In the scanning electron photomicrograph of the treated porcelain surface, hydrofluoric acid etched group appeared the highest roughness. The shear bond strength of the phosphoric acid etched group was not significantly(p>0.05) different between feldspathic porcelain and pressable porcelain. But in no treatment and roughened with a bur group, the shear bond strength of the feldspathic porcelain was significantly higher than that of the pressable porcelain. In hydrofluoric acid etched group, the shear bond strength of the pressable porcelain was significantly higher(p<0.05). Conclusion: 1. Treatment groups showed significantly greater shear bond strengths than no treatment group(p<0.05). 2. Group with more roughened porcelain surface did not always show higher shear bond strengths. 3. In phosphoric acid etched group, there was no significant difference in shear bond strength between feldspathic porcelain and pressable porcelain(p>0.05). However in the other groups, there were significant differences in shear bond strengths between feldspathic porcelain and pressable porcelain(p<0.05).

• 구강회복응용과학지
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• 제22권2호
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• pp.149-159
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• 2006

Statement of problem. Porcelain repair mainly involves replacement with composite resin, but the bond strength between composite resin and all-ceramic coping materials has not been studies extensively. Purpose. The objective of this study was to investigate the influence of composite resin and ceramic etching pattern on shear bond strength of Empress2 ceramic and observe the change of microstructure of ceramic according to etching methods. Material and methods. Eighty-five cylinder shape ceramic specimens (diameter 5mm, IPS Empress 2 core materials) embeded by acrylic resin were used for this study. The ceramic were specimens divided into sixteen experimental groups with 5 specimens in each group and were etched with phosphoric acid(37%, 65%) & hydrofluoric acid (4%, 9%) according to different etching times(30s, 60s, 120s 180s). All etched ceramic surfaces were examined morphologically using SEM(scanning electron microscopy). Etched surfaces of ceramic specimens were coated with silane (Monobond-S) & adhesive(Heliobond) and built up composite resin using Teflon mold. Accomplished specimens were tested under shear loading until fracture on universal testing machine at a crosshead speed 1mm/min; the maximum load at fracture(kg) was recorded. Shear bond strength data were analyzed with one way ANOVA and Duncan tests.(P<.05) Results. Maximum shear bond strength was $30.07{\pm}2.41(kg)$ when the ceramic was etched with 4% hydrofluoric acid at 120s. No significant difference was found between phosphoric etchant group and control group with respect to shear bond strength. Conclusion. Empress 2 ceramic surface was not etched by phosphoric acid, but etched by hydrofluoric acid.

• 대한치과보철학회지
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• 제38권2호
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• pp.169-177
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• 2000

The purpose of this study was to compare the retention of complete cast crown over amalgam ores, composite resin cores, and cast gold cores when cemented with three different luting agents. Eighteen core specimens each of amalgam(Bestaloy, Dong Myung, Seoul, Korea), composite resin (Z100, 3M Dental product, st. Paul, Minn) and type IV gold alloy (Ba-4, Heesung Engelhard Corp., Korea) were made in a customized milling stainless steel die. A wax pattern with a loop attached to occlusal surface was made for each core and a type II gold alloy casting was fabricated. The castings which had clinically acceptable marginal fit were used as test samples. The following luting cements were used to cement cast crowns on each core material : (1) zinc phosphate cement (Confi-dental Products Co., USA) (2) glass-ionomer cement (Fuji Plus, GC Industrial Corp., Tokyo, Japan) (3) resin cement (Panavia 21, Kuraray Co., USA). All cements were mixed according to manufacturers' instructions. A static load of 5kg was then applied for 10 minutes on the crowns. All specimens were stored in saline solution for 24 hours at $37^{\circ}C$ and thermocycled for 500 cycles. After storage and cycling, the tensile bond strengths were measured by using a universal testing machine (Instron Corp., Canton, Mass.) at a crosshead speed of 0.5mm/min. The results were as follows 1. The retentive strength of resin cement was the highest of alt three types of cement for resin core (p<0.05). 2. There was no statistical difference among the retentive strengths of three cements for amalgam core (p>0.05). 3. The retentive strength of resin cement was higher than that of zinc phosphate for cast core, but there was no difference between the retentive strength of glass ionomer cement and those of rein and zinc phosphate cement. 4. The retentive strength of the zinc phosphate cement for amalgam core was the highest of all type of cores.