• 설비공학논문집
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• 제28권7호
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• pp.275-282
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• 2016

MILD (Moderate and Intense Low-oxygen Dilution) combustion using oxygen as an oxidizer is considered as one of the most promising combustion technologies for high energy efficiency and for reducing nitrogen oxide and carbon dioxide emissions. In order to investigate the effects of nozzle angle and oxygen velocity conditions on the formation of oxygen-MILD combustion, numerical and experimental approaches were performed in this study. The numerical results showed that the recirculation ratio ($K_V$), which is an important parameter for performing MILD combustion, was increased in the main reaction zone when the nozzle angle was changed from 0 degrees to 15 degrees. Also, it was observed that a low and uniform temperature distribution was achieved at an oxygen velocity of 400 m/s. The perfectly invisible oxy-MILD flame was observed experimentally under the condition of a nozzle angle of $10^{\circ}$ and an oxygen velocity of 400 m/s. Moreover, the NOx emission limit was satisfied with NOx regulation of less than 80 ppm.

• Tribology and Lubricants
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• 제36권3호
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• pp.117-123
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• 2020

In this study, the effect of the pre-mild wear mode test condition on the subsequent severe wear behavior of carbon steel has been investigated when the wear mode is varied according to the sliding speed change during sliding contact. Two sliding speeds of 0.3 m/s and 3 m/s for the mild wear mode test have been chosen and a sliding speed of 1 m/s for the severe wear mode test. A mild wear mode test at two different sliding speeds has been carried out during the severe wear mode test and total sliding distance of the mild wear mode test has been changed at this time. As a result, it could be found that the wear rate of carbon steel under the severe wear mode test after performing a pre-mild wear mode test is significantly reduced, compared with that before performing. However, its wear rate was slightly higher than that under the mild wear mode test. Oxides produced during the pre-mild wear mode test have been found to play a significant role in reducing the wear rate under the subsequent severe wear mode test. In particular, it was found that the effect of a pre-mild wear mode test performed at the sliding speed of 3 m/s has more rapid and the reduction in the wear rate was greater than thst at the sliding speed of 0.3 m/s.

• 한국주조공학회지
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• 제20권4호
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• pp.230-239
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• 2000

High pressure wear characteristics of DCI(Ductile Cast Iron) were investigated through unlubricated pin-on-disc wear test. Wear test were carried out at speed of 23m/min, under pressure of 3MPa and 3.3 MPa. Cu and/or Mn were added to examine the effect of alloying elements on the high pressure wear characteristics of DCI. To investigate the relationship between wear characteristics and mechanical properties of DCI, Brinell hardness and V-notched Charpy impact energy were tested. Wear surface of each specimen was observed by SEM to determine the wear mechanism of DCI under high pressure wear condition. In the mild wear region, wear characteristics of alloyed DCI specimens were very similar to that of unalloyed DCI. But mild-severe wear transition was occurred at different wear distance and wear rate of DCI specimens were changed by alloying elements. In severe wear condition, wear rate of DCI was dramatically increased by the addition of Mn. Although the addition of Cu 0.46wt% did not decrease the wear rate of DCI in the severe wear region, but it delayed the mild-severe wear transition. Under high pressure wear condition, wear rate and mild-severe wear transition were not concerned with hardness of DCI specimens, but they were deeply associated with impact energy changed by alloying elements.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2015년도 제51회 KOSCO SYMPOSIUM 초록집
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• pp.267-268
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• 2015

The multi-environment probability density function model has been applied to simulate the turbulent $CH_4/H_2$ flames under MILD conditions. The direct quadrature method of moments (DQMOM) has been adopted to solve the transport PDF equation due to its computational efficiency and robustness. The IEM model represents the micromixing process. The numerical results obtained in this study are precisely compared with experimental data in terms of unconditional means and conditional means for scalar field including temperature and species mass fraction.

• 대한기계학회논문집A
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• 제26권3호
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• pp.576-585
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• 2002

A three-dimensional Lagrangian explicit time-integration finite element code for analyzing the dynamic impact phenomena was developed. It uses four node tetrahedral elements. In order to consider the effects of strain rate hardening, strain hardening and thermal softening, which are frequently observed in high-velocity deformation phenomena, Johnson-Cook model is used as constitutive model. For more accurate and robust contact force computation, the defense node contact algorithm was adopted and implemented. In order to evaluate the performance of the newly developed three-dimensional hydrocode NET3D, numerical simulations of the oblique impact of mild steel plate by mild steel sphere were carried out. Ballistic limit about various oblique angle between 0 degree and 80 degree was estimated through a series of simulations with different initial velocities of sphere. Element eroding by equivalent plastic strain was applied to mild steel spheres and targets. Ballistic limits and fracture characteristics obtained from simulation were compared with experimental results conducted by Finnegan et al. From numerical studies, the following conclusions were reached. (1) Simulations could successfully reproduce the key features observed in experiment such as tensile failure termed "disking"at normal impacts and outwards bending of partially formed plus segments termed "hinge-mode"at oblique impacts. (2) Simulation results fur 60 degrees oblique impact at 0.70 km/s and 0.91 km/s were compared with experimental results and Eulerian hydrocode CTH simulation results. The Lagrangian code NET3D is superior to Eulerian code CTH in the computational accuracy. Agreement with the experimentally obtained final deformed cross-sections of the projectile is excellent. (3) Agreement with the experimental ballistic limit data, particularly at the high-obliquity impacts, is reasonably good. (4) The simulation result is not very sensitive to eroding condition but slightly influenced by friction coefficient.

• 충청수학회지
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• 제27권1호
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• pp.89-97
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• 2014

We study the existence of mild solutions for neutral differential equations with nonlocal conditions in the ${\alpha}$-norm.

• 대한수학회지
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• 제57권1호
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• pp.61-88
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• 2020

In this paper, we investigate the existence of mild solutions for a class of fractional impulsive evolution equation with periodic boundary condition by means of the method of upper and lower solutions and monotone iterative method. Using the theory of Kuratowski measure of noncompactness, a series of results about mild solutions are obtained. Finally, two examples are given to illustrate our results.

• Journal of Applied Biological Chemistry
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• 제59권1호
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• pp.69-74
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• 2016

시금치에 fumaric acid와 mild heat의 병합처리를 통해 병원성 미생물 제어효과를 규명하고자 시금치에 E. coli O157:H7, L. monocytogenes 를 접종한 후 각 단일처리 후 미생물 수 변화를 측정하였다. Fumaric acid (0.1, 0.3, 0.5%)와 mild heat (40, 50, $60^{\circ}C$)의 각 단일처리 실험 결과를 토대로, 병합처리를 위한 fumaric acid의 최적농도는 0.5%, mild heat 처리조건으로 $50^{\circ}C$에서 5 min으로 선정하였고, 병합처리 시 L. monocytogenes, E. coli O157:H7의 수는 대조구에 비해 각각 2.53, 2.62 log CFU/g 감소하였다. 그리고 신선한 시금치에 병합처리 후 $4^{\circ}C$에서 12일간 저장하면서 미생물 수 감소 및 품질 변화를 조사하였다. 시금치의 초기 미생물 수에 있어서 대조구와 비교하여, 병합 처리구에서 총 호기성 균을 2.77 log CFU/g 감소시켰다. 특히, 저장 12일 후 병합 처리구의 총 호기성 균 수는 4.84 log CFU/g으로 대조구와 비교하여 1.82 log CFU/g의 감균 효과를 가졌다. 또한 시금치의 저장 중 Hunter 색도 값 및 비타민 C 함량에 있어서 처리구 간의 유의적인 차이를 보이지 않았다. 따라서 본 연구 결과, fumaric acid와 mild heat의 병합처리가 시금치의 미생물학적 안전성 유지에 효과적인 처리라고 판단된다.

• Journal of Audiology & Otology
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• 제24권2호
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• pp.91-98
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• 2020

Background and Objectives: This study aimed to compare functional hearing with the use of a personal sound amplification product (PSAP) or a basic hearing aid (HA) among sensorineural hearing impaired listeners. Subjects and Methods: Nineteen participants with mild-to-moderate sensorineural hearing loss (SNHL) (26-55 dB HL; pure-tone average, 0.5-4 kHz) were prospectively included. No participants had prior experience with HAs or PSAPs. Audiograms, speech intelligibility in both quiet and noisy environments, speech quality, and preference were assessed in three different listening conditions: unaided, with the HA, and with the PSAP. Results: The use of PSAP was associated with significant improvement in pure-tone thresholds at 1, 2, and 4 kHz compared to the unaided condition (all p<0.01). In the quiet environment, speech intelligibility was significantly improved after wearing a PSAP compared to the unaided condition (p<0.001), and this improvement was better than the result obtained with the HA. The PSAP also demonstrated similar improvement in the most comfortable levels compared to those obtained with the HA (p<0.05). However, there was no significant improvement of speech intelligibility in a noisy environment when wearing the PSAP (p=0.160). There was no significant difference in the reported speech quality produced by either device or in participant preference for the PSAP or HA. Conclusions: The current result suggests that PSAPs provide considerable benefits to speech intelligibility in a quiet environment and can be a good alternative to compensate for mild-to-moderate SNHL.

• 대한청각학회지
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• 제24권2호
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• pp.91-98
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• 2020

Background and Objectives: This study aimed to compare functional hearing with the use of a personal sound amplification product (PSAP) or a basic hearing aid (HA) among sensorineural hearing impaired listeners. Subjects and Methods: Nineteen participants with mild-to-moderate sensorineural hearing loss (SNHL) (26-55 dB HL; pure-tone average, 0.5-4 kHz) were prospectively included. No participants had prior experience with HAs or PSAPs. Audiograms, speech intelligibility in both quiet and noisy environments, speech quality, and preference were assessed in three different listening conditions: unaided, with the HA, and with the PSAP. Results: The use of PSAP was associated with significant improvement in pure-tone thresholds at 1, 2, and 4 kHz compared to the unaided condition (all p<0.01). In the quiet environment, speech intelligibility was significantly improved after wearing a PSAP compared to the unaided condition (p<0.001), and this improvement was better than the result obtained with the HA. The PSAP also demonstrated similar improvement in the most comfortable levels compared to those obtained with the HA (p<0.05). However, there was no significant improvement of speech intelligibility in a noisy environment when wearing the PSAP (p=0.160). There was no significant difference in the reported speech quality produced by either device or in participant preference for the PSAP or HA. Conclusions: The current result suggests that PSAPs provide considerable benefits to speech intelligibility in a quiet environment and can be a good alternative to compensate for mild-to-moderate SNHL.