• Journal of Intelligence and Information Systems
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• v.29 no.3
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• pp.167-183
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• 2023

In the recent field of recommendation systems, various studies have been conducted to model sparse data effectively. Among these, GLocal-K(Global and Local Kernels for Recommender Systems) is a research endeavor combining global and local kernels to provide personalized recommendations by considering global data patterns and individual user characteristics. However, due to its utilization of kernel tricks, GLocal-K exhibits diminished performance on highly sparse data and struggles to offer recommendations for new users or items due to the absence of side information. In this paper, to address these limitations of GLocal-K, we propose the GEase-K (Global and EASE kernels for Recommender Systems) model, incorporating the EASE(Embarrassingly Shallow Autoencoders for Sparse Data) model and leveraging side information. Initially, we substitute EASE for the local kernel in GLocal-K to enhance recommendation performance on highly sparse data. EASE, functioning as a simple linear operational structure, is an autoencoder that performs highly on extremely sparse data through regularization and learning item similarity. Additionally, we utilize side information to alleviate the cold-start problem. We enhance the understanding of user-item similarities by employing a conditional autoencoder structure during the training process to incorporate side information. In conclusion, GEase-K demonstrates resilience in highly sparse data and cold-start situations by combining linear and nonlinear structures and utilizing side information. Experimental results show that GEase-K outperforms GLocal-K based on the RMSE and MAE metrics on the highly sparse GoodReads and ModCloth datasets. Furthermore, in cold-start experiments divided into four groups using the GoodReads and ModCloth datasets, GEase-K denotes superior performance compared to GLocal-K.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.150-155
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• 2000

Exhaust emissions from vehicles are the main source of air pollution. Many researchers are trying to find the way of reducing vehicle emissions, especially in the cold transient period of the FTP-75 test. In this study, UEGI (Unburned Exhaust Gas Ignition) technology, warming up the close-coupled catalytic converter (CCC) by igniting the unburned exhaust mixture using two glow plugs installed in the upstream of the catalyst, was developed. It was applied to an exhaust system with a hydrocarbon adsorber to ensure an effective reduction of HC emission during the cold start period. Results showed that the CCC reaches the light-off temperature (LOT) in a shorter time compared with the baseline exhaust system, and HC and CO emissions are reduced significantly during the cold start.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.3
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• pp.94-101
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• 2008

Since regulations of exhaust emissions are continuously reinforced, studies to reduce harmful emissions during the cold start period of SI engines have been carried out very extensively worldwide. During the cold start period, raising the temperature of cold exhaust gas is a key strategy to minimize the light-off time of three way catalysts. In this study, a synthetic gas containing a large amount of hydrogen was injected into the exhaust manifold to raise the exhaust gas temperature and to reduce harmful emissions. The authors tried to evaluate changes in exhaust gas temperature and harmful emissions through controlling the engine operating parameters such as ignition timings and lambda values. Also the authors investigated both combustion stability and reduction of harmful emissions. Experimental results showed that combustion of the synthetic gas in the exhaust manifold is a very effective way for solving the problems of harmful emissions and light-off time. The results also showed that the strategy of retarded ignition timings and increased air/fuel ratios with ESGI is effective in raising exhaust gas temperature and reducing harmful emissions. Futhermore, the results showed that engine operating parameters ought to be controlled to lambda = 1.2 and ignition timing = $0{\sim}3^{\circ}$ conditions to reduce harmful emissions effectively under stable combustion conditions.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.1
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• pp.69-75
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• 2016

This paper covers the result of construction and start-up tests of the KSLV(Korea Space Launch Vehicle)-II combustion chamber hot-firing test facility. This facility was constructed from 2012 to 2014. Start-up test of this facility began in the second half of 2014. Oxidizer cold flow test, fuel cold flow test and cooling water cold flow test were carried out as start-up test. Afterward, ignition test of combustion chamber was accomplished. The result of ignition test is applied to set up start-up sequence of KSLV-II combustion chamber and utilized as base line data for hot-firing test of low and normal design point.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.90-90
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• 2017

Cold spray (Cold gas dynamic spray, kinetic spray) is the latest spray coating process that is known as solid state deposition process. In cold spray, inert gases (typically nitrogen and helium) accelerate powder particles prior to impact onto the substrate. Accelerating particles start to deposit onto the substrate after reaching certain critical velocities depending on the coating materials and substrate. Since process gas temperatures are kept below to melting temperature of the coating materials, it is possible to spray temperature sensitive materials such as copper and titanium, nanocrystal materials, and amorphous metals without affecting the phase change and oxide formation. It is also possible to deposit thick coatings because cold spray coatings present compressive residual stresses. This ability to deposit thick coatings is suitable to repair or rebuild parts as an additive manufacturing process. In this presentation, cold spray is introduced and compared to other additive manufacturing processes such as laser and electron beam based processes. It is also presented some applications especially in the view point of additive manufacturing process.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.47-50
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• 2008

The sub-zero cold is a major environmental consideration for the operational readiness of FCEVs because fuel cells produce water and utilize wet air with varying water content to generate electricity. Typical fuel cells thus have a fatal flaw in freezing conditions at startup. This drawback becomes more serious with the outsourced fuel cell that is entirely water-based for its internal humidification. In this background, the HMC's self-designed fuel cell was developed as an alternative and was employed in the Tucson-based FCEV in 2006 demonstrating its good cold-startup characteristics. The cold-startup capacity of the vehicle was validated through tests in the cold chamber and on the road, resulting in 50% stack power achieved in 250 seconds at $-15^{\circ}C$.

• Journal of Korea Multimedia Society
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• v.25 no.8
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• pp.1242-1250
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• 2022

When recommending cold items that do not have user-item interactions to users, even we adopt state-of-the-arts algorithms, the predicted information of cold items tends to have lower accuracy compared to warm items which have enough user-item interactions. The lack of information makes for recommender systems to recommend monotonic items which have a few top popular contents matched to user preferences. As a result, under-diversified items have a negative impact on not only recommendation diversity but also on recommendation accuracy when recommending cold items. To address the problem, we adopt a diversification algorithm which tries to make distributions of accumulated contents embedding of the two items groups, recommended items and the items in the target user's already interacted items, similar. Evaluation on a real world data set CiteULike shows that the proposed method improves not only the diversity but also the accuracy of cold item recommendation.

• KIISE Transactions on Computing Practices
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• v.22 no.6
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• pp.278-283
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• 2016

Due to explosive increase in the amount of data produced recently, cloud storage system is required to offer high and stable performance. However, VM (Virtual Machine) migration may result in lowered storage service performance. Especially, in an environment where the host-side flash cache is used in a cloud system, the existing warmed up cache is lost and the problematic cold start begins at a new cache due to a VM migration. In this paper, we first demonstrate and analyze the cold start problem and then propose Cachemior (Cache migrator) which enables efficient hot start of the flash cache.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.133-140
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• 2009

A fast-response $CO_2$ analyzer has been developed for measuring the $CO_2$ concentration during transient condition of a SI engine. The analyzer consists of the non-dispersive infrared absorption method, electrical chopping system and water cooling system. The analyzer has good repeatability, linearity and permissible drift characteristic. Besides, it showed 18ms of a response to measure the $CO_2$ concentration. The fast-response $CO_2$ analyzer was applied to a single cylinder SI engine and the $CO_2$ emission was examined during engine start. Simultaneously, the standard exhaust gas analyzer, which has slow response time, was used for confirming the accuracy of the exhaust gas analysis using the fast-response $CO_2$ analyzer. The developed analyzer showed much faster responsive characteristic than that of a standard analyzer and made cycle by cycle exhaust gas analysis possible. The transient engine operating characteristics will be estimated from the $CO_2$ concentration of engine-out emissions and engine operating variables.

• Journal of ILASS-Korea
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• v.28 no.3
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• pp.150-155
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• 2023

Cold-start emissions are given great importance under the Euro-7 emission standard due to their significant impact on overall vehicle emissions. When an engine is started from a cold state, the combustion process is not yet optimized, leading to higher emissions. Hybrid vehicles, in particular, may face additional challenges, as their engine may remain inactive for extended periods, causing their catalysts to cool down and potentially become less effective in reducing emissions. In the present study, the performance of an electric heater was investigated as a means to enhance the catalyst heating during the start-up time. A simulation tool was utilized to develop a model for the gasoline exhaust aftertreatment system. The result indicates that the heater was able to increase the three-way catalyst temperature to 500℃ in 4 s using 20 kW power. In addition, the implementation of a secondary air supply resulted in reduced temperature overshoot and improved conversion efficiencies.