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이동언(Dongeun Lee),이설하(Sulha Lee),이창진(Changjin Lee) 한국추진공학회 2014 한국추진공학회 학술대회논문집 Vol.2014 No.5
후방연소 하이브리드는 기존 하이브리드와 비슷한 연소과정을 가지고 있지만, 1차 연소에서 농후연소 가스를 생성하며 여기에 추가적으로 (2차적으로) 들어오는 산화제와 2차 연소를 하는 과정을 갖는다. 본 연구는 1단계 목표인 하이브리드 시스템을 적용한 농후 연소 가스 생성이다. 기존 연구들을 바탕으로 당량비 3 이상, 가스온도 1500 K 이하를 목표범위로 설정하였다. 그리고 연료 길이, 연료포트 지름, 연료 타입, 산화제 타입을 바꿔가며 당량비에 영향을 미치는 인자를 실험을 통해 확인하였다. 결과적으로, PMMA연료와 본 실험 조건으로는 최대 당량비 1.69, 가스온도 1970 K 인 농후 연소 가스를 생성하였다. Afterburner hybrid has similar combustion process as classical hybrid, but generating fuel-rich gas and additional oxidizer is added in an afterburning combustion chamber. The main objective of current study is to demonstrate and evaluate the performance improvement comparing to classical hybrid. To do this, first goal is to generate fuel-rich gas with hybrid rocket system with target equivalence ratio of 3 or larger and gas temperature of less than 1500 K, which based on formal studies related to fuel-rich gas generator. To make fuel-rich gas, this study performed tests with different equivalence ratio affecting parameters such as fuel length, fuel port diameter, fuel type and oxidizer type. As a result, with use of PMMA fuel and limitation of experimental set-up, maximum equivalence ratio of 1.69 and gas temperature of 1970 K are presented.
Design of a mobile video streaming system using adaptive spatial resolution control
Heejung Lee,Yonghee Lee,Jonghun Lee,Dongeun Lee,Heonshik Shin IEEE 2009 IEEE TRANSACTIONS ON CONSUMER ELECTRONICS - Vol.55 No.3
<P>An efficient mobile video streaming system needs to cope with unstable network bandwidth and limited battery life. We propose a novel streaming system which jointly considers picture quality, bit-rate and energy consumption. Reducing the spatial resolution of a video stream adaptively proves to be more efficient in terms of picture quality and energy consumption than conventional rate control using only adjustment of quantization parameter. We apply the same scheme to scalable coding for large-scale mobile video streaming. This extends the adaptation of an SVC stream to lower bit-rates, while maintaining temporal stability. Our approach has been shown to improve picture quality by approximately 0.5 dB in low bit-rate conditions, and also reduces energy consumption by more than 50% compared to conventional video streaming.</P>
A Scalable and Flexible Repository for Big Sensor Data
Dongeun Lee,Jaesik Choi,Heonshik Shin IEEE 2015 IEEE SENSORS JOURNAL Vol.15 No.12
<P>Data generation rates of sensors are rapidly increasing, reaching a limit such that storage expansion cannot keep up with the data growth. We propose a new big data archiving scheme that handles the huge volume of sensor data with an optimized lossy coding. Our scheme leverages spatial and temporal correlations inherent in typical sensor data. The spatio-temporal correlations, observed in quality adjustable sensor data, enable us to compress a massive amount of sensor data without compromising distinctive attributes in sensor signals. Sensor data fidelity can also be decreased gradually. In order to maximize storage efficiency, we derive an optimal storage configuration for this data aging scenario. Experiments show outstanding compression ratios of our scheme and the optimality of storage configuration that minimizes system-wide distortion of sensor data under a given storage space.</P>
Lee Tae-Hoon,Choi Dongeun,Lee Woosub 한국CDE학회 2021 Journal of computational design and engineering Vol.8 No.6
Robot-assisted surgery has been extensively applied in various microsurgical disciplines owing to its enhanced accuracy and dexterity based on the motion-scaling function between a hand and a surgical instrument. However, the surgical robot system developed thus far incurs high manufacturing costs and restricted compatibility due to the complicated control system, including many actuators and sensors. This paper proposes a novel passive mechanism for motion scaling based on the pantograph structure to resolve these drawbacks of robotic assistance devices. As a first step, a design configuration featuring gravity compensation and the duplication of directional motion is suggested. Subsequently, the geometric dimensions required to satisfy the surgical space and structural constraints are defined. Moreover, the mass of elements required to enable gravity compensation is calculated using moment equations. After determining the principal design parameters, the motion scaling of the proposed passive model is identified using a three-dimensional computer-aided design. In addition, for an extremely precise operation in microsurgery, the dynamic reaction force is expected to be constant in any location. Therefore, to investigate dynamic dexterity, the mathematical model is formulated based on the Lagrangian dynamic equation. Then, the dynamic workspace range is analysed from the determinant of the mass matrix. In addition, the analysis results are evaluated through comparative simulations in different workspace ranges; hence, a constant reaction force can be achieved only in the dynamic workspace range.
Cryptotia recurrence lowering technique with additional acellular dermal matrix graft
Lee, Dongeun,Kim, Young Seok,Roh, Tai Suk,Yun, In Sik Korean Cleft Palate-Craniofacial Association 2019 Archives of Craniofacial Surgery Vol.20 No.3
Background: Cryptotia is a congenital anomaly in which the upper part of the retroauricular sulcus is absent and buried underneath the temporal skin. Various surgical techniques have been reported for the correction of cryptotia following Kubo's V-Y plasty in 1933. Conventional methods using a local skin flap, skin grafting, tissue expansion, Z-plasty, and any of these combined approaches can result in skin deficiency of the upper auricle. The aim of this study was to develop a new method that improves cosmetic results and has fewer complications. Methods: This study involved four patients in whom five cryptotia deformities were corrected using V-Y plasty and Z-plasty. After elevation of the flap, acellular dermal matrix (ADM; MegaDerm) that was over 5 mm in thickness was applied to the cephalo-auricular angle and positioned to enhance the projection of the ear. Lastly, the flap was transposed to complete the repair. Results: Between January 2014 and February 2018, cryptotia correction with ADM graft was performed in four patients. None of the patients developed a recurrence of cryptotia, and there were no postoperative complications such as wound infection, seroma formation, and dehiscence. In addition, the procedures resulted in a favorable cosmetic appearance. Conclusion: Based on these findings, i.e., no recurrence and a favorable cosmetic result, when using an ADM graft, it is suggested that this technique could be an alternative method of cryptotia correction. It could also lessen donor-site morbidity when compared to autologous cartilage grafting and be more cost-effective than using cartilage from a cadaver.
Ultrasonic dissection versus electrocautery for immediate prosthetic breast reconstruction
Lee, Dongeun,Jung, Bok Ki,Roh, Tai Suk,Kim, Young Seok Korean Society of Plastic and Reconstructive Surge 2020 Archives of Plastic Surgery Vol.47 No.1
Background Ultrasonic dissection devices cause less thermal damage to the surrounding tissue than monopolar electrosurgical devices. We compared the effects of using an ultrasonic dissection device or an electrocautery device during prosthetic breast reconstruction on seroma development and short-term postoperative complications. Methods We retrospectively reviewed the medical records of patients who underwent implant-based reconstruction following mastectomy between March 2017 and September 2018. Mastectomy was performed by general surgeons and reconstruction by plastic surgeons. From March 2017 to January 2018, a monopolar electrosurgical device was used, and an ultrasonic dissection device was used thereafter. The other surgical methods were the same in both groups. Results The incidence of seroma was lower in the ultrasonic dissection device group than in the electrocautery group (11 [17.2%] vs. 18 [31.0%]; P=0.090). The duration of surgery, total drainage volume, duration of drainage, overall complication rate, surgical site infection rate, and flap necrosis rate were comparable between the groups. Multivariate analysis revealed that the risk of seroma development was significantly lower in the ultrasonic dissection device group than in the electrocautery group (odds ratio for electrocautery, 3.252; 95% confidence interval, 1.242-8.516; P=0.016). Conclusions The findings of this study suggest that the incidence of seroma can be reduced slightly by using an ultrasonic dissection device for prosthesis-based breast reconstruction. However, further randomized controlled studies are required to verify our results and to assess the cost-effectiveness of this technique.