Enhancement of Anticancer Efficacy of Natural Killer Cells by Optimizing Hydrophilic/hydrophobic Balance o Biomaterials for Cell Surface Coating

Wonjeong LEE,Sungjun KIM,Kyobum KIM 한국생물공학회 2023 한국생물공학회 학술대회 Vol.2023 No.10

The tectonic setting and age of the Neoproterozoic sedimentary and igneous rocks in the Gogunsan islands

Wonjeong Kim,Changwhan Oh,Jinseok Kim,Seunghwan Lee,Jiwan Jeong 대한지질학회 2019 대한지질학회 학술대회 Vol.2019 No.10

Droplet Formation and Unsteady Pressure Oscillation in Hybrid Rocket Combustion

Wonjeong Hyun(현원정),Changjin Lee(이창진) 한국항공우주학회 2021 한국항공우주학회 학술발표회 논문집 Vol.2021 No.11

The effect of hip abductor fatigue on static balance and gait parameters

( Wonjeong Hwang ),( Jun Ha Jang ),( Minjin Huh ),( Yeon Ju Kim ),( Sang Won Kim ),( In Ui Hong ),( Mi Young Lee ) 물리치료재활과학회 2016 Physical therapy rehabilitation science Vol.5 No.1

Objective: Hip abductors play a role in providing stability and movement to the lower limbs. The purpose of this study was to examine the effects of hip abductor fatigue on static balance and gait in the general population. Design: One group pre-test post-test design. Methods: Thirteen university students in their twenties volunteered for the study and had underwent a functional assessment. To induce fatigue, the subjects were instructed to raise their dominant lower extremity up against a load of 50% of 1 repetition maximum while producing hip abduction in a side-lying position. Subjects were instructed to maintain an abduction speed of 30 repetitions per minute to induce fatigue. Muscle fatigue was considered to be established when subjects were unable to perform hip abduction three consecutive times along with the metronome. A post-test of balance and gait was performed immediately in order to prevent fatigue recovery. The center of pressure (COP) distance area was measured using the Zebris FDM-S Multifunction Force measuring plate. Gait performance was analyzed using the GAITRite. Results: The COP distance was increased after fatigue was induced. There was a significant increase in the standard deviation of the medio-lateral and antero-posteror distance (p<0.05). Although there was no significant difference in gait parameters, there was a significant decrease in single support time after fatigue was induced (p<0.05). Conclusions: There was an increase in static balance instability and a significant decrease in single support time during gait due to hip abductor muscle fatigue.

다중점 연결에 적용하는 피드백에 근거한 반응적 폭주 제어 방식의 공정성

최원정(WonJeong Choi),이미정(MeeJeong Lee) 한국정보과학회 1997 한국정보과학회 학술발표논문집 Vol.24 No.1A

ATM 방식은 전통적으로 예방적인 폭주 제어를 채택하였으나, 버스티한 데이터와 같은 트래픽을 지원하는데 있어 대역폭의 효율적인 활용을 위하여 피드백에 따라 송신자의 출력률을 적응적으로 조정하는 폭주 제어 방식을 도입하기 시작하였다. 이러한 반응적 폭주 제어 방색에 관한 연구는 점-대-점 연결을 지원하기 위한 방식으로부터 시작하여 점-대-다중점 연결을 지워하기 위한 방향으로 확장 진행되고 있다. 그런데 반응적 폭주 제어에서 사용되는 피드백의 효율성은 전파 지연에 의하여 크게 좌우되기 때문에 점-대-점 연결의 경우로부터 전파 지연이 성능에 미치는 영향이 연구되어 왔다. 특히, 역량 및 폭주 정도가 각각인 다수의 경로 및 수신자가 존재하는 점-대-다중점의 경우는 송신자료 부터의 거리에 따라 수신자들이 송신자에 미칠 수 있는 영향력이 달라질 수 있어 공정성의 문제도 야기될 수 있다. 본 논문은 시뮬레이션을 통하여 반응적 폭주 제어 방식의 구체적인 구현에 따라 이러한 영향력이 어떻게 달라지는가를 알아보았다. 시뮬레이션 결과는 피드백 인터벌의 크기가 적을수록 불공정성이 더 커지고, 송신자가 피드백을 통합하는 방식에 따라서도 불공정성의 정도가 달라짐을 보여주었다.

생활화학제품 내 금속나노물질 분석

황원정(Wonjeong Hwang),송명기(Myoungki Song),유근배(Keunbai Yoo),김현아(Hyun-A Kim),박다정(Dajeong Park),이병태(Byung-Tae Lee) 환경독성보건학회 2017 한국독성학회 심포지움 및 학술발표회 Vol.2017 No.10

수중대향충돌 방식을 이용한 숙신산 무수물 개질 β-키틴 나노섬유의 제조

진정호,Lee Jongmin,Seo Wonjeong,Song Myeong-Oh,Oh Eunchan 한국키틴키토산학회 2022 한국키틴키토산학회지 Vol.27 No.2

In this study, we report on the production of succinylated β-chitin nanofibers (ChNF) via aqueous counter collision (ACC) method. Succinic anhydride (SA) mediated chemical modification is known as an effective nanofibrillation strategy for typical natural polysaccharides through the surface carboxylation, which has attracted attention due to its relatively mild characterisitics, such as non-toxicity. Using the combined physico-chemical treatment of SA and ACC, the succinylated β-chitin nanofiber (β-SChNF) was successfully prepared as a uniform hydrocolloidal suspension. The SEM and AFM analysis showed that the diameter of the SChNF ranged from 14 nm to 30 nm. The XRD and FT-IR analysis were used to confirm that the original crystal and chemical structure of chitin were maintained even after the physico-chemical nanofibrillation. We also fabricated a transparent film from the SChNF which showed a typical diameter-dependent optical transmittance; that is, the higher the number of ACC pass (i.e., smaller diameter of SChNF), the greater the optical transparency (80%). Our results show that SA chemical pre-treatment of β-chitin can boost successful nanofibrillation.

스월 분사와 삽입연료에 의한 하이브리드 로켓 연소의 저주파수 연소불안정 조절

현원정(Wonjeong Hyun),이창진(Chanjin Lee) 한국항공우주학회 2021 韓國航空宇宙學會誌 Vol.49 No.2

하이브리드 로켓 연소에서 산화제 스월 분사는 회전방향 속도성분이 경계층 유동에 영향을 미쳐 연소안정화에 기여한다. 그러나 스월 강도가 증가할수록 연소성능을 과도하게 변화시키는 문제점이 나타난다. 따라서 참고문헌[7]의 삽입연료와 함께 사용하여 연소성능 변화를 최소화 하면서 연소불안정 억제를 시도하였다. 이를 위해, 일련의 실험을 계획하여 스월 강도와 삽입연료 위치를 변화하며 연소불안정의 발생과 연소성능 변화를 관찰하였다. 실험결과, 스월 각 6°, 삽입연료 위치 310 mm 조합에서 연소불안정이 억제되었으며 연소압력, O/F 비 그리고 연료 후퇴율 등의 변화가 최소인 것으로 확인하였다. 또한 고주파수 대역의 압력진동(p)와 열방출진동(q)의 위상차가 π/2로 음의 결합을 형성하도록 연소조건을 유지하는 것이 저주파수 연소불안정 발생을 억제하는 필요충분조건임을 재확인하였다. In hybrid rocket combustion, the oxidizer swirl injection is frequently used to stabilize the combustion as the rotational velocity component affects the boundary layer flow. However, as the swirl strength increases, a problem arises where the combustion performance changes too much. Thus, this study attempts to control the low frequency instability while minimizing the change in combustion performance by adapting attenuated swirl injection with fuel insert used in reference [7]. To this end, a series of experimental tests were performed by varying swirl intensity and the location of the fuel insert. In the tests, the occurrence of combustion instability and combustion performance were closely monitored. The results confirmed that combustion instability was successfully suppressed at the condition of the swirl angle 6 degree and the location of fuel insert 310 mm. And, the changes in combustion pressure, O/F ratio, and fuel regression rate were found as minimal compared to the baseline case. Also the results reconfirmed that the formation of positive coupling between two high frequency oscillations in 500 Hz band, combustion pressure(p) and heat release oscillation(q), is the necessary and sufficient condition of the occurrence of low frequency instability.

파라핀-왁스를 사용하는 하이브리드 로켓 연소의 비정상 압력 진동

현원정(Wonjeong Hyun),이창진(Changjin Lee) 한국항공우주학회 2022 韓國航空宇宙學會誌 Vol.50 No.5

하이브리드 로켓의 후연소실(post chamber)은 액화된 연료의 추가적 연소를 유도하여 엔탈피 상승으로 이어지도록 한다. 후연소실이 있는 하이브리드 로켓에 파라핀 왁스를 연료로 사용하는 경우, 연소초기에만 비정상 연소 압력진동이 관찰된다. 본 연구는 비정상 연소 압력진동의 발생과 액적의 추가적 연소 사이의 상관관계를 확인하는 것을 목적으로 하고 있다. 이를 위해 후연소실 연소를 가시화하고 POD 기법을 활용한 이미지 분석을 수행하였다. 또한 모드 재구성을 통해 액적의 거동을 포함하고 있는 모드를 분리하여 비정상적인 연소압력의 진동과 액적의 연소 사이의 상관관계를 조사하였다. 일련의 실험에서는 후연소실로 유입되는 액화 연료량과 액적발생을 조절하여 비정상 연소압력 진동의 변화를 유도하였다. 실험결과에 의하면 파라핀 왁스의 연소 초기에만 관찰되는 비정상 연소압력 진동은 후연소실에서 발생하는 액적의 추가적인 연소가 그 발생원인임을 알 수 있다. The post chamber in hybrid rocket is installed to induce additional increase in combustion enthalpy by allowing continuous burning of the liquefied fuels. When paraffin wax fuel is used, unsteady pressure oscillations are observed only at the beginning of combustion. This study intends to investigate the effect of additional combustion of liquefied fuel droplets on the occurrence of unsteady pressure fluctuations. For this, the combustion in post-chamber was visualized and image analysis using POD(Proper Orthogonal Decomposition) technique was performed. In addition, the hypothesis was proposed on the occurrence of unsteady pressure oscillations by identifying the modes including the behavior of droplets through mode reconstruction. Conducting a series of combustion tests, the amount of liquefied fuel flowing into the post chamber and the generation of fuel droplets were controlled. Also, the changes in frequency characteristic of unsteady pressure oscillation were monitored. As a result, the unsteady pressure oscillations observed in paraffin wax combustion were the result of additional combustion of fuel droplets generated in the post chamber.

Accelerate the Shift to Green Energy with PVDF Based Piezoelectric Nanogenerator

Jeonghyeon Lee,Sugato Hajra,Swati Panda,Wonjeong Oh,Yumi Oh,Hyoju Shin,Yogendra Kumar Mishra,Hoe Joon Kim 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.11 No.1

The two greatest difficulties humanity faces are environmental catastrophe and air degradation, and renewable energy from the ocean, solar, and wind offers a possible answer. This research describes a piezoelectric energy harvester (PENG) for harvesting low-frequency water wave energy. The poled PENG device based on a ferroelectric polymer polyvinylidene fluoride (PVDF) delivers a voltage of 32 V and a current of 130 nA. The PENG achieves a power of 1.38 µW at 500 MΩ. The low-frequency vibrations generated from the laboratory equipment were effectively converted into usable electrical energy. Furthermore, the output performance of four PVDF-based PENG units connected in parallel was placed inside a 3D printed housing after being exposed to water waves delivered a voltage of 1.1 V and current of 170 nA. This work presents an efficient approach for gathering low-frequency wave energy and realizing the blue-energy dream. This study offers a cost-effective approach for gathering low-frequency water wave energy and realizing the blue-energy vision.