• Journal of the Korean Institute of Gas
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• v.27 no.3
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• pp.52-58
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• 2023

With the increasing awareness of the importance of carbon neutrality in response to global climate change, the utilization of hydrogen as a carbon-free fuel source is also growing. Hydrogen is commonly used in fuel cells (FC), but it can also be utilized in internal combustion engines (ICE) that are based on combustion. Particularly, ICEs that already have established infrastructure for production and supply can greatly contribute to the expansion of hydrogen energy utilization when it becomes difficult to rely solely on fuel cells or expand their infrastructure. However, a disadvantage of utilizing hydrogen through combustion is the potential generation of nitrogen oxides (NOx), which are harmful emissions formed when nitrogen in the air reacts with oxygen at high temperatures. In particular, for the EURO-7 exhaust regulation, which includes cold start operation, efforts to reduce exhaust emissions during the warm-up process are required. Therefore, in this study, the characteristics of nitrogen oxides and fuel consumption were investigated during the warm-up process of cooling water from room temperature to 88℃ using a 2-liter direct injection spark ignition (SI) engine fueled with hydrogen. One advantage of hydrogen, compared to conventional fuels like gasoline, natural gas, and liquefied petroleum gas (LPG), is its wide flammable range, which allows for sparser control of the excessive air ratio. In this study, the excessive air ratio was varied as 1.6/1.8/2.0 during the warm-up process, and the results were analyzed. The experimental results show that as the excessive air ratio becomes sparser during warm-up, the emission of nitrogen oxides per unit time decreases, and the thermal efficiency relatively increases. However, as the time required to reach the final temperature becomes longer, the cumulative emissions and fuel consumption may worsen.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.8
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• pp.950-955
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• 2007

Non-point source control system which had been designed only for oil-water separation in the fields of oil refinery and garage was upgraded in this research for the removal of runoff pollutants in impervious urban area. Pollutants including oil from driveway and bridge were eliminated by two types of pathway in the system. One is the coalescence mechanism that the oil droplets in the runoff come into contact with each other in the spiral buoyant media surface and form larger coalesced droplets of oil that are carried upstream to the oil layer. The other is the precipitation that solids in runoff were settled by gravity in the system. In this research, coalescing characteristics of oil and water separation were investigated through image analyses, and efficiencies of the non-point source control system were evaluated using dust in driveway and waste engine oil. Media made of high density and high molecular weight polyethylene was indeterminate helical shape and had sleek surface by analysing SEM photographs and BET. Surface area and specific gravity of media which were measured directly were 1,428 $mm^2$ and 45.3 $kg/m^3$ respectively. From the image analyses of the oil droplets photographs which were taken by using microscope, it was proved clearly that the coalescence was the main pathway in the removal of oil from the runoff. Finally, the performances of the non-point source control system filled up with the media were suspended solid $86.6\sim95.2%$, $COD_{Cr}$, $87.3\sim95.4%$, n-Hexane extractable materials $71.8\sim94.8%$ respectively.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.227-233
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• 2007

Carbon/carbon (C/C) composites as unique materials possess exceptional thermal resistance with light weight, high stiffness, and strength even at high temperature. However, one serious obstacle for application of the C/C composites is their poor oxidation resistance in high temperature oxidizing environments. SiC coating has been employed to protect the composites from oxidation. This study explored combustion characteristics of 4-directional (4D) carbon/carbon composites using liquid fuel rocket engine to investigate ablative motion of the materials. C/C composites were made of coal tar pitch as a matrix precursor, and heat-treated at $2300^{\circ}C$. Throughout repeated densification process, the density of the material reached $1.903g/cm^3$. After machining 4D C/C composites, the nozzle surface was coated by a SiC layer by pack-cementation method to improve oxidation resistance. Erosion characteristics of SiC-coated C/C composites were measured as function of the ratio of oxygen to fuel. The morphological change of the composites after combustion test was investigated using SEM and erosion mechanism also was discussed.

• Science of Emotion and Sensibility
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• v.15 no.2
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• pp.177-182
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• 2012

Automotive sub-mat carpet for convenience and comfort of floor administration is additional supplemented floor mat. Sub Mat Backing of the current vehicle's materials reclaimed rubber, PVC, etc. are used, but secondary rubber and PVC Backing have bad sound absorption. Also rubber is heavy too. Contact surfaces between PET staple fiber, PET non-woven, PVC backing and car's floor carpet was measured the coefficient of friction for each sub-mat's non-slip evaluation. A surface of PET non-woven sub-mat has the highest coefficient of friction. Each of sample was observed by optical microscope the contact surfaces before and after. Contact surfaces of PET staple fiber sub-mat was changed increasingly to non-woven. This fact is shown that the sub-mat would be tangled between its contact surface and top of the floor carpet. It is expected to be highly non-slip. In case of PET non-woven sub-mat had not different for contact surfaces between before and after. And PVC backing was shown lower non-slip than other samples. The result of optical microscope and coefficient of friction is seems to be related.

• Journal of Digital Convergence
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• v.16 no.8
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• pp.169-179
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• 2018

Recently, web search query information has been applied in advanced predictive model research. Google dominates the global web search market in the Korean market; however, Naver possesses a dominant market share. Based on this characteristic, this study intends to compare the utility of the Korean web search query information of Google and Naver using predictive models. Therefore, this study develops three time-series predictive models to estimate the youth unemployment rate in Korea using the ARIMA model. Model 1 only used the youth unemployment rate in Korea, whereas Models 2 and 3 added the Korean web search query information of Naver and Google, respectively, to Model 1. Compared to the predictability of the models during the training period, Models 2 and 3 showed better fit compared with Model 1. Models 2 and 3 correlated different query information. During predictive periods 1 (continuous with the training period) and 2 (discontinuous with the training period), Model 3 showed the best performance. During predictive period 2, only Model 3 exhibited a significant prediction result. This comparative study contributes to a general understanding of the usefulness of Korean web query information using the Naver and Google search engines.

• Particle and aerosol research
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• v.13 no.3
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• pp.105-110
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• 2017

Real-time measurements of fine particles from stack emission gases are necessary due to the needs of continuous environmental monitoring of PM10 and PM2.5. The porous tube dilutor using hot and cold dilutions was developed to measure fine particles without condensable particles from highly humid emission gases and compared to the commercialized ejector-type dilutor. Particle size distributions were measured at the emission gases from a diesel engine and a coal-fired boiler. The porous tube dilutor could successfully measure the accumulation mode particles including relatively large particles more than $3{\mu}m$ without nuclei particles, while the ejector dilutor detected some condensable particles and could not detect large particles. The porous tube dilutor could successfully remove the already condensed water droplet particles generated by a humidifier in a $30m^3$ chamber.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• v.10 no.2
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• pp.59-63
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• 2005

가. 자율주행 트랙터가 작업하는 동안 작동상태를 효과적으로 모니터링하고 제어할 수 있도록 하기 위해 인터넷을 통한 자율주행 트랙터의 모니터링과 원격제어 기술에 대하여 시험 하였다. 나. 트랙터를 모니터링하고 제어하는 곳과 경작지가 있는 곳을 인터넷으로 연결하고, 운전자가 탑승하지 않은 트랙터는 인터넷을 통해 전달받은 명령을 수행하도록 액튜에이터를 제어하고 제어되는 상황을 경작지에 위치한 카메라가 촬영하여 인터넷을 통하여 원격지의 운전자 쪽으로 전송하도록 시스템을 구성했다. 다. HST 트랙터 조종장치로서 서보제어가 가능한 액튜에이터를 개발 장착하고 제어성능을 시험하였다. 전자유압제어(EHPS)식 조향액튜에이터는 , 조향가능각 100도의 전범위에 조향 제어가 가능했으며 전조향에 필요한 시간은 약 1.6초 정도 였다. 피스톤 펌프의 사판각을 제어하는 전후진 제어기는 리니어 모터 구동식으로 총 제어 변위 50mm를 이동하는데 제어시간이 약 1.2초 소요되었다. 엔진 회전수를 제어하기위한 스로틀 액튜에이터는 리니어 모터 구동식으로 제어변위 30mm에 대해 제어시간이 0.8초 소요되었다. 3점 링크에 부착된 작업기의 위치를 제어하는 리프트 제어기도 리니어모터로 구동하였으며 제어거리 40mm에 대해 제어시간 0.9초정도가 소요되었다 라. 제작된 HST 무인 트랙터를 인터넷과 무선통신 시스템을 이용하여 원격 모니터링과제어 가능성에 대해 시험 했다. 인터넷을 통한 장거리 원격제어 및 모니터링 시험에서 제어신호의 전달지연은 0.3 ${\sim}$ 0.5초정도로 제어신호의 피이드 백을 확인할 때까지는 약1초정도의 대기 시간이 필요한 것으로 나타나 모니터링 및 제어 시스템의 개발 시 이를 고려할 설계가 필요한 것으로 나타났다.된 표층수온 분포값보다 2005년 2월에 관측된 표층수온 분포값이 상대적으로 낮은 분포 특성을 나타내고 있었다. 따라서 인공위성자료를 이용한 황해의 2004년 해황 분석 결과는 이상수온 상승의 원인이 쿠로시오 해류의 변동과 관련성이 높다고 판단되며 이에 대한 지속적인 연구가 현재 진행중에 있다.에 인산염 처리, 여기에 초음파 처리, 마지막 단계로 3분 끓이면 억제율이 68%까지 억제되었다. 이는 단일처리시 전혀 억제를 못하는 처리를 단계별로 한 단계씩 더해가면 allergy 억제효과가 나타난다고 할 수 있겠다. 초음파 처리도 역시 저 allergy 처리 공정에 이용될 수 있는데 이것은 그 처리로 인해 새로운 알러젠이 생성될 수도 있다. 또한 복합처리로 allergy를 감소시키면 연속적이고 동시적으로 하기 때문에 원가를 절감할 수 있다.환경현안에 대한 정치경제적 접근을 외면하지 말고 교과서 저작의 소재로 삼을 수 있어야 하며, 이는 '환경관리주의'와 '녹색소비'에 머물러 있는 '환경 지식교육'과 실천을 한단계 진전시키는 작업으로 이어질 것이다. 이후 10년의 환경교육은 바로 '생태적 합리성'과 '환경정의'라는 두 '화두'에 터하여 세워져야 한다.배액에서 약해를 보였으나, 25% 야자지방산의 경우 50 ${\sim}$ 100배액 어디에서도 액해를 보이지 않았다. 별도로 적용한 시험에서, 토마토의 경우에도 25% 야자지방산 비누 50 ${\sim}$ 100배액 모두 약해를 발생하지 않았으나, 오이에서는 25% 야자지방산 비누 100배액에도 약해를 나타내었다. 12. 이상의 결과, 천연지방산을 이용하여 유기농업에 허용되는 각종의 살충비누를 제조할 수 있었으며, 방제가 조사결과 진딧물, 응애 등 껍질이 연약한

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.7
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• pp.677-687
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• 2017

Aircraft can often be exposed to a variety of environments and vibrations such as engine, hydraulic pump, aerodynamic force. These may cause cracking and destruction of the mechanical structure and sub-components by high-cycle fatigue. The axial piston type pump which is usually applied to the aircraft hydraulic pump can be necessarily accompanied by the fluid pulsation by continuous rotation of the axial piston. The fatigue crack was identified at the dampener fitting welding zone to prevent vibration damping during the running of aircraft equipped with this type of pulsation hydraulic pump. In order to understand the root cause of this matter, fracture and component analyses were carried out and also integral type dampener fitting was applied to prevent recurrence of the crack as a subject of design improvements. Structural integrity stress analysis, fatigue analysis, qualification test and aircraft system equipped test was conducted to verify the design validity in application to integral type dampener fitting. The test results were sufficiently satisfactory with the demand lifetime of the material from the various types of test as conducted and the subject of design improvement in this study could be objectively evaluated that shall be applied to the operational aircraft.

• Proceedings of the Korea Inteligent Information System Society Conference
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• 2000.04a
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• pp.357-364
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• 2000

기존의 웹 디자인은 웹이라는 매체의 특성 상 디자인적인 요소가 매우 중요함에도 불구하고 디자인은 위한 구체적인 방법론이 미약하다. 특히, 많은 소비자들을 유인하고 구매를 촉발시켜야 하는 인터넷 쇼핑몰의 경우에는 더욱 더 그럼하에도 불구하고 이를 위한 전략적인 방법론이 부족하다. 즉, 기존 연구들은 제품의 다양성, 서비스, 촉진, 항해량, 편리성, 사용자 인터페이스 등이 중요하다고 하였지만 실제 인터넷 쇼핑몰을 디자인하는 입장에서는 활용하기가 상당히 애매하다. 그 이유는 이들 요인들은 서로 영향관계를 가지고 있어서 사용자 인터페이스가 복잡하면 항해량이 늘어나 편리성이 감소하고, 제품이 늘어나더라도 검색엔진을 사용하면 상대적으로 항해량이 감소하게 되어 편리성이 증가한다. 따라서, 이들 요인을 활용하여 인터넷 쇼핑몰을 구축하려면 요인간의 영향관계를 면밀히 파악하고 이 영향요인이 소비자의 구매행동에 어떠한 영향을 주는지가 충분히 검토되어야 한다.이에 본 연구에서는 퍼지인식도를 이용하여 인터넷 쇼핑몰 상에서 소비자의 구매행동에 영향을 주는 요인을 추출하고 이들 요인간의 인과관계를 도출하여 보다 구체적이고 전략적으로 인터넷 쇼핑몰을 디자인할 수 있는 방법으로 web-Cogmulator를 제시한다. Web-Cogmulator는 소비자의 쇼핑몰에 대한 암묵지식 형태의 구매행동을 형태지식화하여 지식베이스 형태로 가지고 있기 때문에 인터넷 쇼핑몰의 다양한 요인의 변화에 따른 소비자의 구매행동을 추론 시뮬레이션하는 것이 가능하다. 이에 본 연구에서는 기본적인 인터넷 쇼핑몰 시나리오를 바탕으로 추론 시뮬레이션을 실시하여 Web-Cogmulator의 유용성을 검증하였다.를, 지지도(support), 신뢰도(confidence), 리프트(lift), 컨빅션(conviction)등의 관계를 통해 다양한 방법으로 모색해본다. 이 연구에서 제안하는 이러한 개념계층상의 흥미로운 부분의 탐색은, 전자 상거래에서의 CRM(Customer Relationship Management)나 틈새시장(niche market) 마케팅 등에 적용가능하리라 여겨진다.선의 효과가 나타났다. 표본기업들을 훈련과 시험용으로 구분하여 분석한 결과는 전체적으로 재무/비재무적 지표를 고려한 인공신경망기법의 예측적중률이 높은 것으로 나타났다. 즉, 로지스틱회귀 분석의 재무적 지표모형은 훈련, 시험용이 84.45%, 85.10%인 반면, 재무/비재무적 지표모형은 84.45%, 85.08%로서 거의 동일한 예측적중률을 가졌으나 인공신경망기법 분석에서는 재무적 지표모형이 92.23%, 85.10%인 반면, 재무/비재무적 지표모형에서는 91.12%, 88.06%로서 향상된 예측적중률을 나타내었다.ting LMS according to increasing the step-size parameter $\mu$ in the experimentally computed. learning curve. Also we find that convergence speed of proposed algorithm is increased by (B+1) time proportional to B which B is the number of recycled data buffer without complexity of computati

• The KIPS Transactions:PartB
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• v.14B no.7
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• pp.513-522
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• 2007

Clustering is to divide given data and automatically find out the hidden meanings in the data. It analyzes data, which are difficult for people to check in detail, and then, makes several clusters consisting of data with similar characteristics. On-Line Document Clustering System, which makes a group of similar documents by use of results of the search engine, is aimed to increase the convenience of information retrieval area. Document clustering is automatically done without human interference, and the number of clusters, which affect the result of clustering, should be decided automatically too. Also, the one of the characteristics of an on-line system is guarantying fast response time. This paper proposed a method of determining the number of clusters automatically by geometrical information. The proposed method composed of two stages. In the first stage, centers of clusters are projected on the low-dimensional plane, and in the second stage, clusters are combined by use of distance of centers of clusters in the low-dimensional plane. As a result of experimenting this method with real data, it was found that clustering performance became better and the response time is suitable to on-line circumstance.