• 한국자동차공학회논문집
• /
• 제18권5호
• /
• pp.136-144
• /
• 2010

Exhaust gas recirculation (EGR) is an emission control technology allowing significant NOx emission reduction from light-and heavy duty diesel engines. The future EGR type, dual loop EGR, combining features of high pressure loop EGR and low pressure loop EGR, was developed and optimized by using a commercial engine simulation program, GT-POWER. Some variables were selected to control dual loop EGR system such as VGT (Variable Geometry Turbocharger)performance, especially turbo speed, flap valve opening diameter at the exhaust tail pipe, and EGR valve opening diameter. Applying the dual loop EGR system in the light-duty diesel engine might cause some problems, such as decrease of engine performance and increase of brake specific fuel consumption (BSFC). So proper EGR rate (or mass flow) control would be needed because there are trade-offs of two types of the EGR (HPL and LPL) features. In this study, a diesel engine under dual loop EGR system was optimized by using design of experiment (DoE). Some dominant variables were determined which had effects on torque, BSFC, NOx, and EGR rate. As a result, optimization was performed to compensate the torque and BSFC by controlling start of injection (SOI), injection mass and EGR valves, etc.

• 한국음향학회지
• /
• 제21권3호
• /
• pp.293-303
• /
• 2002

본 논문에서는 ITU G.729 음성 복호화기와 듀얼 SOLA (Synchronized Overlap-Add)알고리듬을 통합한 최적의 음성 속도 변환시스템 (TSM)을 구현한다. 제안된 시스템은 ITU G.729 음성 복호화기를 통한 8 Khz 80 샘플/프레임 단위의 음성 신호를 입력으로 가정하여 듀얼 SOLA를 통해 사용자가 원하는 음성 속도에 맞추어 출력, 음성을 천천히 혹은 빠르게 최적화된 음성 품질로의 재생을 가능하게 한다. 특히 본 논문에서 제안된 듀얼 SOLA는 다양한 SOLA 파라미터에 대한 모의실험과 이론적 분석에 의거하여 ITU G.729 복호화기 음성 신호에 대한 최적화된 음성 재생 변환 기능을 제공하며, 입력 음성신호의 부가적인 인터폴레이션 (interpolation) 과정을 첨가하여 최대 2배 빠르기 혹은 2배 느리기의 극한 속도율에서도 우수한 성능의 통합 음성 속도 변환 시스템을 구현할 수 있다. 제안된 시스템은 다양한 입력 음성신호와 재생 속도에 대한 모의실험을 걸쳐 그 성능을 검증한다.

• 상하수도학회지
• /
• 제14권3호
• /
• pp.260-270
• /
• 2000

The objective of this study is to evaluate the effect of filter aids in the dual-media rapid filtration. Paper-filter tests were conducted to determine the proper dosages of coagulant and filter aid, and pilot plant tests using two dual-media filter columns were performed for a variety of filtration rates. Using a filter aid (non-ionic polymer), the maximum feasible filtration rate is 480m/day, while turbidity is less than 0.3 NTU and filter run-time is about 70 hours. It is possible to increase the filtration rate up to 360 m/day for keeping the turbidity less than 0.1 NTU. Turbidity increases for the filtration rate greater than 360m/day. In general, the quality of filtered water with a filter aid is stable, while the filter maintains a sufficient filter run-time for a maximum allowable head loss. Particularly, the initial breakthrough can be effectively controlled. The use of a filter aid may be one of the methods applicable if the turbidity of filtered water is required to be improved or if the filter breakthrough limits filter run-time.

• ETRI Journal
• /
• 제36권4호
• /
• pp.625-634
• /
• 2014

This paper studies a dual-hop multiple-access relay network where two independent source nodes transmit information to a common destination node with the aid of multiple single-antenna amplify-and-forward relays. Each relay node is subject to an individual power constraint. We focus on the design of distributed beamforming schemes for the relays to support the transmission rate requirements of the two sources. To this end, we first characterize the achievable rate region for this network via solving a sequence of corner point optimization problems proposed in this paper. We also develop several low-complexity suboptimal schemes in closed form. Two inner bounds of the achievable rate region are theoretically shown to be approximately optimal in two special scenarios. Finally, numerical results demonstrate the effectiveness of our proposed approaches.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
• /
• pp.149-152
• /
• 2012

The laboratory experiments have been conducted to investigate the effects of air preheated temperature on the emission characteristics by a model gas turbine burner with a hybrid/dual swirl jet flames configuration. The concentration of NOx and CO emissions, and flue gas temperature at combustor exit were measured with varying the equivalence ratio for different air preheated temperatures of 300, 400, 500K at atmospheric pressure. It was overall shown that the NOx and CO emissions, and flue gas temperature were decreased according to the decreasing of equivalence ratio due to the effects of lean premixed combustion regardless of the air preheated temperature. Experimental results of a lean premixed flames configuration indicated that the NOx emission was increased with higher inlet air temperature and air flow rate, which is attributed to the increasing of flue gas temperature and heat release related to the thermal NOx mechanism. But the CO emission was shown the opposite tendency, that is, the CO emission was decreased with increasing of inlet air temperature and flow rate.

• 한국기계가공학회지
• /
• 제20권11호
• /
• pp.17-23
• /
• 2021

A cyclone is a dust-separating mechanism that works on the principle of centrifugal force. The performance of a cyclone is evaluated using pressure loss and collection efficiency. A multi-cyclone arrangement is used to improve the collection efficiency within a limited area. In this study, experiments and numerical analyses were conducted on a dual arrangement of mini-hydrocyclone separators, which was fabricated using 3D printing. The experiment was performed at an inlet flow rate of 0.7 m/s, and alumina powder with a particle size of 0.5, 15, and 50 ㎛. ANSYS FLUENT, was used for the numerical analysis. The reliability of the numerical analysis was verified through a comparison with the experimental results. The errors in the experiment and numerical analysis were confirmed to be 2% at the outlet flow rate.

• 한국콘텐츠학회논문지
• /
• 제22권8호
• /
• pp.467-481
• /
• 2022

독일의 이원화체제 직업교육이 청년실업률에 미치는 효과에 대한 논의를 통해서 우리에게 주는 시사점이 무엇이며, 현재 한국 직업교육의 문제점 개선을 위한 방안을 모색하고자 하는 것이 연구의 목적이다. 독일이 '직업교육훈련법'(Berufsbildungsgesetz)을 근거로 시행하고 있는 이원화체제(duales System) 직업교육제도에 대해 어떤 평가를 받고 있는지, 산·학·관의 협력체제에 대한 구체적인 시스템 구축 형태를 알 수 있었으며, 이러한 제도의 위기와 문제점을 제시할 수 있었다. 독일 직업교육의 이원화 제도에 대한 책임은 국가와 각 주의 교육부에 있으며, 기업의 실무 측면에서는 민간기업 및 상공회의소의 관할 책임이 주어진다. 기업에서의 실무는 기능중심의 교육으로 진행되며, 직업학교에서는 능력중심의 이론교육을 받게 된다. 또한 독일 Idustrie 4.0에 맞는 디지털 직업교육훈련(vocational and education training)과 이원화 학위과정을 통한 고등직업교육의 학위취득에 대한 필요성과 요구를 알 수 있었다. 이러한 모든 수준의 이원적 직업교육훈련(VET)과, 대학의 고등직업교육, 직업계속교육 프로그램 등, 기업의 경쟁력 향상을 위한 인적자원의 개발과 활용이 잘 이루어져 청년실업률이 유럽에서 가장 낮은 것을 볼 수 있었다. 우리나라의 직업교육도 학교와 기업이 동시에 직업교육훈련을 할 수 있는 체제 구축을 통해 실업률을 개선할 수 있을 것이다. 특히 직업학교와 기업의 이원화교육을 위해 우리가 가장 중요하게 생각하고 심도 깊은 논의와 협력을 이끌어 내야할 '노·사·정간의 긴밀한 협의'의 필요성을 독일의 경우를 통해 판단할 수 있었다.

• 대한통합의학회지
• /
• 제10권4호
• /
• pp.83-91
• /
• 2022

Purpose: The goal of this study was to investigate changes in dual-task performance according to age and difficulty of cognitive tasks for the in community-dwelling elderly populations, as well as to examine their changes in hand dexterity according to age and cognitive function. Methods: A total of 135 people aged 65 years old and over participated in the study. To evaluate each participant's dual-task performance, each participant completed a dual task. To assess their cognitive function, the Korean Mini-Mental State Examination (MMSE-K) and the Korean version of Montreal Cognitive Assessment (MoCA-K) were the tools used. Participants were divided into three groups based on their age: 65-69 years, 70-79 years, and 80-89 years. Results: The findings showed that age groups and the difficulty of the cognitive task significantly affected the amount of time required for dual-task performance (p<.001). Additionally, the dual-task correct response rate (CRR) decreased significantly with age groups and the difficulty of the cognitive task (p<.001). The amount of time required for finger dexterity performance increased significantly with age groups (mean score±standard deviation [SD]; 19.46±2.26 in subjects aged 65-69 years; 21.92±2.61 in subjects aged 70-79 years; and 23.82±2.92 in subjects aged 80-89 years; p<.001). Moreover, as a result of the correlation between hand dexterity and cognitive function, MoCA-K was -0.563 and MMSE-K was -.412, showing a statistically significant correlation (p<.001). Conclusions: Age and the difficulty of the cognitive task affect the community-dwelling elderly populations in terms of dual-task performance and dual-task CRR. In addition, aging and general cognition have an impact on hand dexterity. Based on the results of this study, it is anticipated that the results will serve as a reference for domestic clinical trials that confirm cognitive decline in the elderly using dual task and hand dexterity evaluation.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2007년도 춘계학술대회 논문집
• /
• pp.421-424
• /
• 2007

Dry sliding wear behavior of ultra-fine grained (UFG) plain low carbon dual phase steel, of which microstructure consists of hard martensite in a ductile ferrite matrix, has been investigated. The wear characteristics of the UFG dual phase steel was compared with that of a coarse grained dual phase steel under various applied load conditions. Dry sliding wear test were carried out using a pin-on-disk type tester at various loads of 1N to 100N under a constant sliding speed condition of 0.20m/s against an AISI 52100 bearing steel ball at room temperature. The sliding distance was fixed as 1000m for all wear tests. The wear rate was calculated by dividing the weight loss, measured to the accuracy of 10-5g by the specific gravity and sliding distance. The worn surfaces and wear debris were analyzed by SEM, EDS and profilometer. Micro-vickers hardness of the cross section of worn surfaces were conducted to analyze strain hardening underneath the contact surfaces. The wear mechanism of the UFG dual phase steel was investigated with emphasis on the unstable nature of the grain boundaries of the UFG microstructure.

• 소성∙가공
• /
• 제16권4호
• /
• pp.299-303
• /
• 2007

Dry sliding wear behavior of ultra-fine grained(UFG) plain low carbon dual phase steel, of which microstructure consists of hard martensite in a ductile ferrite matrix, has been investigated. The wear characteristics of the UFG dual phase steel was compared with that of a coarse grained dual phase steel under various applied load conditions. Dry sliding wear test were carried out using a pin-on-disk type tester at various loads of 1N to 100N under a constant sliding speed condition of 0.20m/s against an AISI 52100 bearing steel ball at room temperature. The sliding distance was fixed as 1000m for all wear tests. The wear rate was calculated by dividing the weight loss, measured to the accuracy of 10-5g by the specific gravity and sliding distance. The worn surfaces and wear debris were analyzed by SEM, EDS and profilometer. Micro-vickers hardness of the cross section of worn surfaces were conducted to analyze strain hardening underneath the contact surfaces. The wear mechanism of the UFG dual phase steel was investigated with emphasis on the unstable nature of the grain boundaries of the UFG microstructure.