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하재석(Jaeseok Ha),김재훈(Jaehoon Kim),정규동(Gyoodong Jung),박재범(Jaebeom Park),양호영(Hoyoung Yang),서보휘(Bohwi Seo) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.2
A crack in a solid propellant increases the area of burning surface, which leads to excessive burning that causes motor failure. Therefore, it is necessary to evaluate fracture toughness of solid propellants. However, it is very difficult to measure fracture toughness of solid propellants because of the nonlinear mechanical behavior. In this study, evaluation of fracture toughness on a solid propellant was carried out under the assumption that the solid propellant is a linear viscoelastic material. Actual displacements from fracture toughness tests using CCT specimens were converted into pseudo-elastic displacements by using stress relaxation characteristics and fracture toughness was evaluated using ASTM E399 standard. Also, effects of test temperature and speed on the fracture toughness were considered.
하재석(Jaeseok Ha),김재훈(Jaehoon Kim),정규동(Gyoodong Jung),박재범(Jaebeom Park),양호영(Hoyoung Yang),서보휘(Bohwi Seo) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11
고체추진제 내부의 균열은 연소면적을 증가시키기 때문에 과연소를 발생시키며 로켓의 기능을 상실하거나 파손되는 문제로 이어질 수 있다. 따라서 고체추진제의 설계에서 균열진전에 대한 저항력인 파괴인성의 평가가 요구된다. 하지만 고체추진제의 특성상 복잡하고 심한 비선형 거동을 나타내기 때문에 파괴인성을 측정하는 데에는 많은 어려움이 있다. 본 연구에서는 고체추진제를 선형점탄성 재료로 가정하여 파괴인성을 평가하였다. CCT(Center-cracked Tension) 시험편을 이용한 파괴인성시험을 수행하였으며 점탄성재료에서 나타나는 응력완화현상을 이용한 가상탄성변위를 계산하여 ASTM E399 규격을 통해 파괴인성을 평가하였다. 또한 파괴인성에 대한 시험온도, 시험속도의 영향에 대한 결과를 고찰하였다. Increased burning area generated by cracks in a solid propellant can lead to excessive burning and failure and severe engine failure. Therefore, it is necessary to evaluate fracture toughness of solid propellants. However, it is very difficult to measure fracture toughness of solid propellants because of the nonlinear mechanical behavior. In this study, fracture toughness evaluation of a solid propellant was conducted assuming that the solid propellant is the linear viscoelastic material. Actual displacements from fracture toughness tests using CCT specimens were converted into pseudo-elastic displacements by using stress relaxation characteristics. Also, effects of test temperature and speed on the fracture toughness were considered.
스마트폰 카메라를 이용한 QR 코드 스캔 과정에서의 사용성 연구
김재석(Jaeseok Kim),서혜승(Hyeseung Seo) 한국HCI학회 2013 한국HCI학회 학술대회 Vol.2013 No.1
QR 코드는 필요한 정보만을 사용자들에게 선택적으로 제공해줄 수 있다는 장점 때문에 주로 기업의 다양한 오프라인 마케팅에 활용되고 있으며, 스마트폰 등 모바일 디바이스의 보급과 더불어 그 활용 또한 서서히 증가하고 있다. 본 연구는 현재 보편적으로 이용되고 있는 스마트폰의 QR 코드 스캔 인터페이스의 사용성을 사용자 조사를 통해 관찰하고자 한다. 연구 결과는 QR 코드에 관련된 서비스 기획자/마케팅 담당자가 QR 코드 스캔을 어려워하는 사용자를 이해할 수 있게 도우며, HCI 관점에서의 개선 방향을 제안한다는 점에서 그 의의가 있다. 실험 결과, 사용자들은 QR 코드 스캔 과정에서 카메라와 QR 코드의 거리 조절에서 어려움을 느끼며, QR 코드 스캔 경험이 없는 사용자들은 QR 코드 스캔 앱을 설치하여 스캔까지 도달하는 과정을 이해하는데 어려움을 겪음을 알 수 있었다. QR code is applied to a variety of offline marketing in company, because it offers necessary information optionally to user. The application of it also increases slowly with suppling mobile device like smartphone. This study covers the usability of interface scanning QR code by smartphone which is used widely through user research. The result will help for service designer and marketer related to QR code to understand users better, and it will be meaningful to suggest improvement in view of HCI. The result of the experiment shows user have difficulty in modulating the distance between the camera and QR code when they tried to scan it. Furthermore we could know that user who have no any experience of scanning QR code have more difficulty in understanding the process from downloading QR reader to scanning QR code.
LiveGantt: Interactively Visualizing a Large Manufacturing Schedule
Jaemin Jo,Jaeseok Huh,Jonghun Park,Bohyoung Kim,Jinwook Seo IEEE 2014 IEEE transactions on visualization and computer gr Vol.20 No.12
<P>In this paper, we introduce LiveGantt as a novel interactive schedule visualization tool that helps users explore highly-concurrent large schedules from various perspectives. Although a Gantt chart is the most common approach to illustrate schedules, currently available Gantt chart visualization tools suffer from limited scalability and lack of interactions. LiveGantt is built with newly designed algorithms and interactions to improve conventional charts with better scalability, explorability, and reschedulability. It employs resource reordering and task aggregation to display the schedules in a scalable way. LiveGantt provides four coordinated views and filtering techniques to help users explore and interact with the schedules in more flexible ways. In addition, LiveGantt is equipped with an efficient rescheduler to allow users to instantaneously modify their schedules based on their scheduling experience in the fields. To assess the usefulness of the application of LiveGantt, we conducted a case study on manufacturing schedule data with four industrial engineering researchers. Participants not only grasped an overview of a schedule but also explored the schedule from multiple perspectives to make enhancements.</P>
A Case of Painful Hashimoto Thyroiditis that Mimicked Subacute Thyroiditis
Hye Mi Seo,Miyeon Kim,Jaeseok Bae,Jo-Heon Kim,Jeong Won Lee,이상아,Gwanpyo Koh,Dae Ho Lee 전남대학교 의과학연구소 2012 전남의대학술지 Vol.48 No.1
Hashimoto thyroiditis (HT) is an autoimmune thyroid disorder that usually presents as a diffuse, nontender goiter, whereas subacute thyroiditis (SAT) is an uncommon disease that is characterized by tender thyroid enlargement, transient thyrotoxicosis, and an elevated erythrocyte sedimentation rate (ESR). Very rarely, patients with HT can present with painful, tender goiter or fever, a mimic of SAT. We report a case of painful HT in a 68-year-old woman who presented with pain and tenderness in a chronic goiter. Her ESR was definitely elevated and her thyroid laboratory tests suggested subclinical hypothyroidism of autoimmune origin. 99mTc pertechnetate uptake was markedly decreased. Fine needle aspiration biopsy revealed reactive and polymorphous lymphoid cells and occasional epithelial cells with Hürthle cell changes. Her clinical symptoms showed a dramatic response to glucocorticoid treatment. She became hypothyroid finally and is now on levothyroxine therapy.
반복적인 굽힘에 따른 FBGA 메모리 모듈의 피로 수명 예측
서경원(Kyoungwon Seo),유수프 츠나르(Yusuf Cinar),장건희(Gunhee Jang),장재석(Jaeseok Jang),구창우(Changwoo Koo) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
In this research, the fatigue life of fine-pitch ball grid array (FBGA) solder joints in memory modules was predicted by the bending experiment and the finite element analysis. Four-point bending test was performed by JEDEC standard to determine fatigue life of a memory module with five packages. Finite element model of the memory module was developed and analyzed under various displacement levels by using direct integration method. Strain under cyclic bending was measured and compared with simulation results for validation of the finite element model of the memory module. A global-local modeling technique was used in finite element simulation to calculate the strain response of the solder joints, and Coffin-Manson equation was developed by experimental and simulation methods. Then, the fatigue life of memory modules was predicted under cumulative damage condition by using the Miner’s rule and compared with experimental results. Experimental results show that predicted fatigue life of the memory module matches with experimental results closely.
Fatigue life estimation of FBGA memory modules under harmonic excitation
Yusuf Cinar,Kyoungwon Seo,Gunhee Jang,Jaeseok Jang,Changwoo Koo 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
This paper predicts the fatigue life of fine-pitch ball grid array (FBGA) solder joints in memory modules due to harmonic excitation by the experiments and the finite element method. A global-local modeling technique was used in finite element simulation. A finite element model of the memory module with simplified solder joints was developed as a global model, and the natural frequencies and modes were calculated and verified by experimental modal testing. Displacement variations were calculated from the global model due to vibration excitation using the mode superposition method. A local model with detailed solder joints was developed in order to calculate stress magnitude concentrated on solder joints of the memory module under vibration. Stress versus life (S-N) curve was developed for memory modules under various vibration levels to derive solder material fatigue constants. Then the fatigue life of the memory module was determined by using the Basquin equation and Miner’s rule. It was experimentally verified that predicted fatigue life of the memory module under cumulative damage conditions matches with experimental results with reasonable accuracy.
Chihun In,Jungmok Seo,Hyukho Kwon,Jeongmook Choi,Sangwan Sim,Jaeseok Kim,Taeyong Kim,Taeyoon Lee,Hyunyong Choi IEEE 2015 IEEE transactions on terahertz science and technol Vol.5 No.4
<P>The surface-trap mediated carrier recombination is a crucial feature in characterizing the optoelectronic properties of nanowires (NWs). Due to the one-dimensional characteristics, the photoexcited carriers experiences multiple carrier interactions in the transverse direction such that strong carrier-carrier interactions are expected to play an important role in the NW carrier recombination. Here, using ultrafast optical-pump and terahertz-probe spectroscopy, we show that the Auger scattering significantly reduces the trap-mediated decay process. Systematic studies on bulk Si, bundled, individual, and encapsulated (reduced surface-trap density) SiNWs reveal that the effect of Auger recombination exhibits strong pump-fluence dependence depending on the surface-treatment condition.</P>