• 한국자동차공학회논문집
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• 제22권4호
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• pp.105-110
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• 2014

This paper presents the hysteresis friction of a sliding elastomer on various types of surfaces. The hysteresis friction is calculated by means of an analytical model which considers the energy spent by the local deformation of the rubber due to surface asperities. By establishing the fractal character of the surfaces, the contribution to rubber friction of roughness at different length scales is accounted for. High resolution surface profilometer is used in order to calculate the main three surface descriptors and the minimal length scale that can contribute to hysteresis friction. The results show that this friction prediction can be used in order to characterize in an elegant manner the surface morphology of various surfaces and to quantify the friction coefficient of sliding rubber as a function of surface roughness, load and speed.

• Reproductive and Developmental Biology
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• 제41권2호
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• pp.41-50
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• 2017

Until today, success in germline cells and tissue cryopreservation is limited mainly due to the poor understanding of the complex physiological processes can lead to cell damage during cryopreservation. Germline cells, from both male and female, have unique ability to differentiate into one or more cell lines and thus it becomes a crucial point to store them in subzero temperature with the minimal damage of their functional properties and maximum recovery of unchanged and viable cells when thawed. In the past three decades, a vast research has been performed using various different animal models which in fact have led to development of new methodologies and optimization of older one. However, successful use of animal model has provided the opportunity in research with human germline cells and tissues preservation, but not in all the cases. Therefore, the use of new cryo-protective chemicals and modified protocols have been often found in different groups of researchers based on the types, physical structures, utility and animal species of the specimens to be cryopreserved. This review discusses about the basics of different types of cryopreservation methodologies and commonly used optimized protocols and cryoprotectants for germline cells and tissues preservation.

• Current Research on Agriculture and Life Sciences
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• 제32권2호
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• pp.67-73
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• 2014

Mulberry fruits were semi-dried using hot air ($60-100^{\circ}C$) or cool air ($20-40^{\circ}C$), and the effects of the drying temperature and processing time on the quality of the final dried mulberry fruits were investigated. Response surface methodology was employed to establish a statistical model and predict the conditions resulting in minimal loss of the total phenolic content (TPC) and ascorbic acid. Thus, using overlapped contour plots, the optimal conditions for producing semi-dried mulberry fruits, which reduced the moisture residue to 45% and minimized the nutrient losses of TPC and ascorbic acid, were determined for the hot-air process ($60.7^{\circ}C$ for 5.4 h) and cool-air process ($34.8^{\circ}C$ for 23.3 h). Plus, a higher drying temperature was found to lead to a faster loss of moisture and ascorbic acid, while the TPC was significantly decreased in the cool-air dried mulberry fruits due to the higher activity of polyphenol oxidase between 30 and $40^{\circ}C$.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권5호
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• pp.1354-1372
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• 2012

Route establishment in Mobile Ad Hoc Network (MANET) is the key mechanism to a successful connection between a pair of source and destination nodes. An efficient routing protocol constructs routing path with minimal time, less routing overhead and capable of utilizing all possible link connectivity. In general, most on-demand MANET routing protocols operates over symmetrical and bidirectional routing path, which is infeasible due to the inherent heterogeneous properties of wireless devices. Simulation results show that the presence of unidirectional links on a network severely affect the performance of a routing protocol. In this paper, a robust protocol independent scheme is proposed, which enable immediate rediscovery of alternative route for a path blocked by a unidirectional link. The proposed scheme is efficient; route rediscovery is locally computed, which results in significant minimization of multiple route packets flooding. Nodes may exploit route information of immediate neighbors using the local reply broadcast technique, which then redirect the control packets around the unidirectional links, therefore maintaining the end-to-end bidirectional connection. The proposed scheme along with Ad Hoc On-demand Distance Vector (AODV) and AODV-Blacklist routing protocol is investigated over three types of mobility models. Simulation results show that the proposed scheme is extremely reliable under poor network conditions and the route connectivity can be improved by as much as 75%.

• International Journal of Aeronautical and Space Sciences
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• 제4권1호
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• pp.88-98
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• 2003

Compared to the noise limits (CAN7) specified in ICAO Annex 16 for civil helicopters, the Lynx helicopter equipped with BERP blades has only 0.2 EPNdB margin in the approach case although it has more than 4 EPNdB margin in fly-over and take-off conditions. The objectives of the study described in this paper were to devise a low noise main rotor blade for the Lynx using UEAF combined with the high resolution airload model ACROT. A design requirement is that the new blade, KBERP (Korean BERP) blade should achieve a significant reduction in noise during approach(at least 6EPNdB margin) without any noise penalty in fly-over and take-off conditions and minimal performance penalty. It was decided to investigate a tip modification to the BERP blade, employing the twin vortex concept to reduce the BVI noise and to retain the excellent high speed performance characteristics of BERP. Through the parametric study, the KBERP blade with optimized twin vortices has at least a 9 EPNdB noise margin in approach flight condition with only a small penalty in fly-over and take-off conditions. The KBERP tip is thus a very cost effective wav to reduce BVI noise during approach.

• Geomechanics and Engineering
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• 제1권3호
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• pp.193-204
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• 2009

A 10.4-m high highway embankment retained behind mechanically stabilized earth (MSE) walls is under construction in the northeastern part of the Indian state of Bihar. The structure is constructed with compacted, micaceous, grey, silty sand, reinforced with polyester (PET) geogrids, and faced with reinforced cement concrete fascia panels. The connections between the fascia panels and the geogrids failed on several occasions during the monsoon seasons of 2007 and 2008 following episodes of heavy rainfall, when the embankment was still under construction. However, during these incidents the MSE embankment itself remained by and large stable and the collateral damages were minimal. The observational data during these incidents presented an opportunity to develop and calibrate a simple procedure for estimating rainfall induced pore water pressure development within MSE embankments constructed with backfill materials that do not allow unimpeded seepage. A simple analytical finite element model was developed for the purpose. The modeling results were found to agree with the observational and meteorological records from the site. These results also indicated that the threshold rainwater infiltration flux needed for the development of pore water pressure within an MSE embankment is a monotonically increasing function of the hydraulic conductivity of backfill. Specifically for the MSE embankment upon which this study is based, the analytical results indicated that the instabilities could have been avoided by having in place a chimney drain immediately behind the fascia panels.

• Archives of Pharmacal Research
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• 제3권1호
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• pp.1-6
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• 1980

As part of our endeavor to increase the productivity of steroid by enzymatic transformation of corticosteroids, attempts have been made to increase the solubility of steroids by using some organic solvents. When the solubility of steroids is the rate limiting factor in the steroid transformation, it was found that the use of solvents significantly improved the yield. Hydrocorisone as a substrate and 3-ketosteroid .DELTA.$^{1}$ dehydrogense as an immobilized whole cell enzyme were employed as the model system for this study. It was found that the yield of product, prodnisolone, goes through a maximum with an increase in the solvent concentration. At a high solvent concentration, the solvent showed a toxic effect and it causes a decrease in the product yield by the second order inhibition mechanism. Among the solvents evaluated, methanol and ethanol were found to be the best. These alcohols are not only good solvents but also showed minimal toxic effect. Based on the experimental results, it was concluded that the productivity of steroid can be increased by usign well selcted solvents systems for the enzymatic transformation of steroids.

• 한국콘텐츠학회논문지
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• 제6권11호
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• pp.126-134
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• 2006

기존의 객체지향 통합 모델링 방법은 전쟁게임 모델을 두 계층으로 구분하여 개발할 수 있는데, 상위계층에서는 객체의 추상화된 행위를 모델링하며 하위계층에서는 모델의 세부적인 행위를 표현하게 된다. 이 방법에서는 시뮬레이션 전문가와 군 관련 전문가가 각각의 계층에서 별도로 작업을 할 수 있는 장점이 있다. 본 논문에서는 통합 모델링을 발전시킨 파라미터 행위 모델링 방법을 이용하여 전쟁 게임 시뮬레이터를 구축할 수 있는 방안을 제시한다. 제안한 방법에서는 군 관련 전문가 또는 사용자가 모델링 방법에 대하여 별도의 지식이 없이도 새로운 알고리즘이나 전략을 시뮬레이터에 추가하거나 수정할 수 있는 장점이 있다. 제안한 방법의 효용성을 보이기 위해 구현된 해군 군함의 전쟁게임 시뮬레이터를 구체적으로 소개한다.

• Journal of Power Electronics
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• 제13권1호
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• pp.59-69
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• 2013

An alternative technique to control multilevel inverters with vector approximations has been presented. The innovative control method utilizes specially designed two-dimensional hysteresis comparators to simplify the implementation and improve the resultant waveform. The multistage inverter designed with maximum number of levels is operated in such a way to approximate the reference voltage vector by exploiting the large number of multilevel inverter vectors. A three-stage inverter with the main high voltage stage made of three phase, six-switch and singly-fed inverter is considered for application to the proposed design. The proposed control concept is to maintain a higher voltage stage state as long as it can lead to a target vector. High and medium voltage stages controllers are based on surface hysteresis comparators to hold the switching state or to perform the necessary change to achieve its reference voltage with minimal switching losses. The low voltage stage controller is designed to approximate the target reference voltage to the nearest inverter vector using the nearest integer rounding and adjustment comparators. Model simulation and prototype test results show that the proposed control technique clearly outperforms the previous control methods.

• KSBB Journal
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• 제9권2호
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• pp.230-237
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• 1994

회전식 여과기는 일종의 분리기로서 동물세포의 연속배양에 이용되어 높은 세포농도와 그와 비례한 높은 생산성을 가져다 준다. 회전식 여과기를 이용한 세포배양은 여러 인자들에 의해 세포농도의 변화가 결정되는데 이를 수학적으로 modeling하고 수치 모사와 sensitivity analysis를 통하여 조사하였다. 고농도 배양시 암모니아의 축적은 세포 성장을 크게 둔화시키고 최대세포농도도 따라서 낮게 된다. 운전 인자 중 세포유치율은 세포 성장속도와 최대세포농도의 크기에 가장 큰 영향을 끼침이 밝혀졌다. 비배지공급속도는 세포농도의 변화에 거의 영향을 끼치지 않으며 배지의 연속식공급과 계단식공급은 세포성장에 큰 차이를 보이지 않는다.