• Nuclear Engineering and Technology
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• 제53권2호
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• pp.583-591
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• 2021

Various compositions of CeO₂-Ce₃Si₂ (0, 10, 30, 50, and 100 wt%Ce₃Si₂) composites were fabricated using conventional sintering and spark plasma sintering. Lower relative density, enhanced interdiffusion of oxygen and silicon, and silicide agglomerations from the congruent melting of Ce₃Si₂ at 1390 ℃ were only observed from conventionally-sintered pellets. Thermal conductivity of spark plasma sintered CeO₂-Ce₃Si₂ composites was calculated from the measured thermal diffusivity, specific heat, and density, which exhibited dense (>90 %TD) and homogeneous microstructure. The composite with 50 wt%Ce₃Si₂ exhibited 55% higher thermal conductivity than CeO₂ at 500 ℃, and 81% higher at 1000 ℃.

• 한국분무공학회지
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• 제27권4호
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• pp.203-210
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• 2022

Combustion and performance of a spark-ignition engine fueled with propane and butane were analyzed under different compression ratio. The electricity efficiencies of propane and butane increased with increasing the electricity production. The heat release rates of propane and butane were similar at a compression ratio of 9:1 because both fuels had similar optimal ignition timings without knocking combustion. Therefore, the difference in electricity efficiencies of engine generators was insignificant. However, at a higher compression ratio of 11:1, the butane engine generator had a lower electricity efficiency than the propane engine generator because its ignition timing retarded to suppress the knocking combustion.

• Journal of information and communication convergence engineering
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• 제20권2호
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• pp.96-102
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• 2022

We aim to build predictive models for Airbnb's prices using a GPU-accelerated RAPIDS in a big data cluster. The Airbnb Listings datasets are used for the predictive analysis. Several machine-learning algorithms have been adopted to build models that predict the price of Airbnb listings. We compare the results of traditional and big data approaches to machine learning for price prediction and discuss the performance of the models. We built big data models using Databricks Spark Cluster, a distributed parallel computing system. Furthermore, we implemented models using multiple GPUs using RAPIDS in the spark cluster. The model was developed using the XGBoost algorithm, whereas other models were developed using traditional central processing unit (CPU)-based algorithms. This study compared all models in terms of accuracy metrics and computing time. We observed that the XGBoost model with RAPIDS using GPUs had the highest accuracy and computing time.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2010년도 춘계학술발표대회
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• pp.33-36
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• 2010

소프트웨어가 대형화되고 복잡해짐에 따라 발생하는 오류가 증가되고 있다. 안전성이 특히 중요시되는 안전필수(safety-critical) 내장형 시스템에서 오류가 발생하면 인명상의 피해 또는 재산상의 피해를 야기한다. 개발 후, 테스팅을 통해 이런 오류를 찾는 비용은 매우 크고, 모든 오류를 찾는 것은 불가능하다고 인식되고 있다. 따라서 소프트웨어 개발단계에서 이런 오류를 탐지하고 제거하려는 노력이 증대되고 있다. 본 논문에서는 SPARK Ada를 사용하여 안전필수 내장형 시스템을 개발할 때, 오류를 제거할 수 있는 흐름분석(flow analysis) 기법을 사용하여 특정한 타입의 오류를 제거할 수 있음을 보인다. 또한 이를 적용하여 안전필수 시스템을 개발한다.

• Archives of Metallurgy and Materials
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• 제63권3호
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• pp.1477-1480
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• 2018

The mechanical behavior and the change of retained austenite of nanocrystalline Fe-Ni alloy have been investigated by considering the effect of various Ni addition amount. The nanocrystalline Fe-Ni alloy samples were rapidly fabricated by spark plasma sintering (SPS). The SPS is a well-known effective sintering process with an extremely short densification time not only to reach a theoretical density value but also to prevent a grain growth, which could result in a nanocrystalline structures. The effect of Ni addition on the compressive stress-strain behavior was analyzed. The variation of the volume fraction of retained austenite due to deformation was quantitatively measured by means of x-ray diffraction and microscope analyses. The strain-induced martensite transformation was observed in Fe-Ni alloy. The different amount of Ni influenced the rate of the strain-induced martensite transformation kinetics and resulted in the change of the work hardening during the compressive deformation.

• Archives of Metallurgy and Materials
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• 제64권3호
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• pp.863-867
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• 2019

The effects of carbon content on the austenite stability and strain-induced transformation of nanocrystalline Fe-11% Ni alloys were investigated using X-ray analysis and mechanical tests. The nanocrystalline FeNiC alloy samples were rapidly fabricated using spark plasma sintering because of the extremely short densification time, which not only helped attain the theoretical density value but also prevented grain growth. The increased austenite stability resulted from nanosized crystallites in the sintered alloys. Increasing compressive deformation increased the volume fraction of strain-induced martensite from austenite decomposition. The kinetics of the strain-induced martensite formation were evaluated using an empirical equation considering the austenite stability factor. As the carbon content increased, the austenite stability was enhanced, contributing to not only a higher volume fraction of austenite after sintering, but also to the suppression of its strain-induced martensite transformation.

• Archives of Metallurgy and Materials
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• 제66권4호
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• pp.1029-1032
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• 2021

WC-Co cemented carbides were consolidated using spark plasma sintering in the temperature 1400℃ with transition metal carbides addition. The densification depended on exponentially as a function of sintering exponent. Moreover, the secondary (M, W) C_x phases were formed at the grain boundaries of WC basal facet. Corresponded, to increase the basal facets lead to the plastic deformation and oriented grain growth. A higher hardness was correlated with their grain size and lattice strain. We suggest that this is due to the formation energy of (M, W)C_x attributed to inhibit the grain growth and separates the WC/Co interface.

• 한국가스학회지
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• 제27권3호
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• pp.1-10
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• 2023

산업혁명의 발달로 인해 급격하게 증가된 온실가스 배출량을 저감하기 위해 배기 배출물 규제가 계속해서 강화되고 있다. 이를 만족시키기 위해선 친환경 연료의 사용은 필수적이다. 미래의 친환경 연료로서 수소가 주목받고 있지만, 물질적 특성으로 인해 취급과 보관에 큰 어려움을 겪고 있어, 이에 대안으로 암모니아가 제안되었다. 암모니아는 수소 대비 상온 조건에서 쉽게 액화가 가능하며, 에너지밀도가 높다. 이에 엔진의 연료로서 암모니아의 적용성을 검토하기 위해 직접분사식 암모니아 전소 엔진에서 연소제어인자의 변경에 따른 실험을 진행하였다. 본 실험은 점화시기(Spark Timing)와 공기과잉률(Excess Air Ratio) 두 개의 변수를 변경하여 실험을 진행하였다.엔진 속도 1,500 RPM 및 중부하 이상(제동 토크 200 Nm)의 조건에서 암모니아 전소를 하였을 때, 연소 안정성과 질소산화물, 미연 암모니아 등의 배기 배출물의 경향을 관찰하였다. 연소제어인자의 최적화를 통해 암모니아만을 연료로 사용한 경우에도 안정적인 연소가 가능한 조건을 찾을 수 있었고, 향후 운전영역 확장을 위한 전략을 적용할 계획이다.

• 한국분말재료학회지
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• 제19권2호
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• pp.127-133
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• 2012

The sintering behaviors and process parameters of some compounds (carbides, oxides, sulfides, borides) were investigated experimentally. These compounds were successfully consolidated and showed high densities. Some unique phenomena such as retardation of grain growth, suppression of thermal decomposition and maintenance of initial non-equilibrium phases, were observed by the proper control of process in spark sintering.

• 오토저널
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• 제5권2호
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• pp.41-47
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• 1983

The analysis shows that the variation of maximum pressure of the cycle, rate of hear release, rate of mass burned, and combustion delay are influenced by the inlet air humidity in the spark-ignition engine. The quantitative combustion delay can be obtained from the rate of mass burned. Also, the variation of time loss and effective compression ratio with the change of inlet air humidity are dominated by the development of rate of heat release.