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Thang Phan,Ha Phan Ai Nguyen,Cao Khoa Dang,Minh Tri Phan,Vu Thanh Nguyen,Van Tuan Le,Binh Thang Tran,Chinh Van Dang,Tinh Huu Ho,Minh Tu Nguyen,Thang Van Dinh,Van Trong Phan,Binh Thai Dang,Huynh Ho Ngo The Korean Society for Preventive Medicine 2023 예방의학회지 Vol.56 No.4
Objectives: The coronavirus disease 2019 (COVID-19) pandemic has increased the workload of healthcare workers (HCWs), impacting their health. This study aimed to assess sleep quality using the Pittsburgh Sleep Quality Index (PSQI) and identify factors associated with poor sleep among HCWs in Vietnam during the COVID-19 pandemic. Methods: In this cross-sectional study, 1000 frontline HCWs were recruited from various healthcare facilities in Vietnam between October 2021 and November 2021. Data were collected using a 3-part self-administered questionnaire, which covered demographics, sleep quality, and factors related to poor sleep. Poor sleep quality was defined as a total PSQI score of 5 or higher. Results: Participants' mean age was 33.20±6.81 years (range, 20.0-61.0), and 63.0% were women. The median work experience was 8.54±6.30 years. Approximately 6.3% had chronic comorbidities, such as hypertension and diabetes mellitus. About 59.5% were directly responsible for patient care and treatment, while 7.1% worked in tracing and sampling. A total of 73.8% reported poor sleep quality. Multivariate logistic regression revealed significant associations between poor sleep quality and the presence of chronic comorbidities (odds ratio [OR], 2.34; 95% confidence interval [CI], 1.17 to 5.24), being a frontline HCW directly involved in patient care and treatment (OR, 1.59; 95% CI, 1.16 to 2.16), increased working hours (OR, 1.84; 95% CI,1.37 to 2.48), and a higher frequency of encountering critically ill and dying patients (OR, 1.42; 95% CI, 1.03 to 1.95). Conclusions: The high prevalence of poor sleep among HCWs in Vietnam during the COVID-19 pandemic was similar to that in other countries. Working conditions should be adjusted to improve sleep quality among this population.
Design of control moment generator for insect-mimicking flapping-wing micro air vehicle
Vu Hoang Phan(판 흐앙 부),Hoon Cheol Park(박훈철) 한국항공우주학회 2014 한국항공우주학회 학술발표회 논문집 Vol.2014 No.11
본 연구에서는 곤충 모방 날갯짓 비행체가 제어 모멘트를 발생할 수 있는 날갯짓면 변경 장치를 설계하고 검토하였다. 날갯짓 장치는 슬라이더-크랭크와 풀리-줄 메커니즘의 조합을 통하여, 장착된 모터의 회전운동을 큰 날갯짓 운동으로 변경할 수 있도록 설계하였다. 날갯짓면 변경 장치는 좌우 날개의 날갯짓 각도는 동일하게 유지하면서도 좌우 날개의 날갯짓면을 독립적으로 수평면에 대하여 7~10 도 정도 변경할 수 있도록 설계하였다. 이 장치는 각 날개의 공기력 방향을 변경할 수 있게 하여 자세 제어를 위한 제어 모멘트를 발생할 수 있다. In this work, we designed and investigated the stroke-plane-change (SPC) mechanism for control moment generation in our flapping-wing micro air vehicle (MAV). The flapping-wing mechanism was designed to transfer the rotational motion from the installed motor to large flapping wing motions through a combination of the slider-crank and pulleystring mechanisms. The SPC mechanism is able to independently modify the flapping stroke-plane up to 10° in the left and right wings while maintaining the same amplitude of flapping angle just like a real beetle. As a result, the direction of the resultant aerodynamic forces in each wing can be changed to generate suitable control moments for attitude control.
Phan, Hoang Vu,Kang, Taesam,Park, Hoon Cheol IOP Publishing 2017 Bioinspiration & biomimetics Vol.12 No.3
<P>An insect-like tailless flapping wing micro air vehicle (FW-MAV) without feedback control eventually becomes unstable after takeoff. Flying an insect-like tailless FW-MAV is more challenging than flying a bird-like tailed FW-MAV, due to the difference in control principles. This work introduces the design and controlled flight of an insect-like tailless FW-MAV, named KUBeetle. A combination of four-bar linkage and pulley-string mechanisms was used to develop a lightweight flapping mechanism that could achieve a high flapping amplitude of approximately 190 degrees. Clap-and-flings at dorsal and ventral stroke reversals were implemented to enhance vertical force. In the absence of a control surface at the tail, adjustment of the location of the trailing edges at the wing roots to modulate the rotational angle of the wings was used to generate control moments for the attitude control. Measurements by a 6-axis load cell showed that the control mechanism produced reasonable pitch, roll and yaw moments according to the corresponding control inputs. The control mechanism was integrated with three sub-micro servos to realize the pitch, roll and yaw controls. A simple PD feedback controller was implemented for flight stability with an onboard microcontroller and a gyroscope that sensed the pitch, roll and yaw rates. Several flight tests demonstrated that the tailless KUBeetle could successfully perform a vertical climb, then hover and loiter within a 0.3 m ground radius with small variations in pitch and roll body angles.</P>
Optimal flapping wing for maximum vertical aerodynamic force in hover: twisted or flat?
Phan, Hoang Vu,Truong, Quang Tri,Au, Thi Kim Loan,Park, Hoon Cheol IOP Publishing 2016 Bioinspiration & biomimetics Vol.11 No.4
<P>This work presents a parametric study, using the unsteady blade element theory, to investigate the role of twist in a hovering flapping wing. For the investigation, a flapping-wing system was developed to create a wing motion of large flapping amplitude. Three-dimensional kinematics of a passively twisted wing, which is capable of creating a linearly variable geometric angle of attack (AoA) along the wingspan, was measured during the flapping motion and used for the analysis. Several negative twist or wash-out configurations with different values of twist angle, which is defined as the difference in the average geometric AoAs at the wing root and the wing tip, were obtained from the measured wing kinematics through linear interpolation and extrapolation. The aerodynamic force generation and aerodynamic power consumption of these twisted wings were obtained and compared with those of flat wings. For the same aerodynamic power consumption, the vertical aerodynamic forces produced by the negatively twisted wings are approximately 10%-20% less than those produced by the flat wings. However, these twisted wings require approximately 1%-6% more power than flat wings to produce the same vertical force. In addition, the maximum-force-producing twisted wing, which was found to be the positive twist or wash-in configuration, was used for comparison with the maximum-force-producing flat wing. The results revealed that the vertical aerodynamic force and aerodynamic power consumption of the two types of wings are almost identical for the hovering condition. The power loading of the positively twisted wing is only approximately 2% higher than that of the maximum-force-producing flat wing. Thus, the flat wing with proper wing kinematics (or wing rotation) can be regarded as a simple and efficient candidate for the development of hovering flapping-wing micro air vehicle.</P>
Phan, Hoang Vu,Truong, Quang Tri,Park, Hoon Cheol IOP Publishing 2017 Bioinspiration & biomimetics Vol.12 No.3
<P>This work presents a parametric study to find a proper wing configuration for achieving economical flight using unsteady blade element theory, which is based on the 3D kinematics of a flapping wing. Power loading was first considered as a performance parameter for the study. The power loadings at each wing section along the wingspan were obtained for various geometric angles of attack (AoAs) by calculating the ratios of the vertical forces generated and the power consumed by that particular wing section. The results revealed that the power loading of a negatively twisted wing could be higher than the power loading that a flat wing can have; the power loading of the negatively twisted wing was approximately 5.9% higher. Given the relatively low average geometric AoA (alpha(A),(root) approximate to 44 degrees and alpha(A),(tip) approximate to 25 degrees), the vertical force produced by the twisted wing for the highest power loading was approximately 24.4% less than that produced by the twisted wing for the strongest vertical force. Therefore, for a given wing geometry and flapping amplitude, a flapping-wing micro air vehicle required a 13.5% increase in flapping frequency to generate the same strongest cycle-average vertical force while saving about 24.3% power. However, when force(3)/power(2) and force(2)/power ratios were considered as performance indices, the twisted wings for the highest force(3)/power(2) (alpha(A),(root) approximate to 43 degrees and alpha(A),(tip) approximate to 30 degrees) and force(2)/power (alpha(A),(root) approximate to 43 degrees and alpha(A,tip) approximate to 36 degrees) required only 6.5% and 4% increases in flapping frequency and consumed 26.2% and 25.3% less power, respectively. Thus, it is preferable to use a flapping wing operating at a high frequency using the geometric AoAs for the highest power loading, force(3)/power(2) ratio, and force(2)/power ratio over a flapping wing operating at a low frequency using a high geometric AoA with the strongest vertical force. Additionally, by considering both aerodynamic and inertial forces, this study obtained average geometric AoAs in the range of 30 degrees to 40 degrees, which are similar to those of a typical hovering insect's wings. Therefore, the operation of an aerodynamically uneconomical, high AoA in a hovering insect's wings during flight is explainable.</P>