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Vu Dinh Quang,Nguyen Dinh Khoa,Nguyen Dinh Duc 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.8
This research examines the influent of structural characteristics (shape, size, material properties, porosity), external conditions (mechanical load, thermal load, and foundation parameters) on the vibration and nonlinear dynamic response of shear deformable porous plates made of functionally graded materials (FGM) in the thermal environment and rested on the Pasternak’s elastic foundation. Reddy’s third-order shear deformation theory (TSDT) and von Kármán’s geometric nonlinearity are used to explore the structural behavior of thick FGM porous plates with two types of porosity distribution in FGM porous plates namely, even and uneven patterns. The solutions are obtained through the Bubnov-Galerkin method and RungeKutta methods. The outcomes are compared with other research in the result section to assess the reliability of the solution method in the paper.
Duc, Nguyen Dinh,Seung-Eock, Kim,Cong, Pham Hong,Anh, Nguyen Tuan,Khoa, Nguyen Dinh Elsevier 2017 International journal of mechanical sciences Vol.133 No.-
<P><B>Abstract</B></P> <P>The purpose of the present study is to investigate dynamic response and vibration of composite double curved shallow shells with negative Poisson's ratios in auxetic honeycombs core layer on elastic foundations subjected to blast and damping loads using analytical solution. This study considers composite double curved shallow shells with auxetic core which have three layers in which the top and bottom outer skins are isotropic aluminum materials; the central layer has honeycomb structure using the same aluminum material. Based on the first order shear deformation theory (FSDT) with the geometrical nonlinear in von Karman and using Airy stress functions method, Galerkin method and the fourth-order Runge–Kutta method, the resulting equations are solved to obtain expressions for nonlinear motion equations. The effects of geometrical parameters, material properties, elastic foundations Winkler and Pasternak, the nonlinear dynamic analysis and vibration of double curved shallow shells with negative Poisson's ratios in auxetic honeycombs core layer are studied.</P> <P><B>Highlights</B></P> <P> <UL> <LI> To investigate dynamic response and vibration of composite double curved shallow shells by using analytical solution. </LI> <LI> The composite shells have the central auxetic core layer—honeycomb structures with negative Poisson's ratio. </LI> <LI> Based on the first order shear deformation theory (FSDT). </LI> <LI> Used airy stress functions, Galerkin method and fourth-order Runge–Kutta method. </LI> <LI> The effects of geometrical parameters, material properties, elastic Winkler and Pasternak foundations, mechanical and blast loads are studied. </LI> </UL> </P>
Synchronization Controller for a 3-RRR Parallel Manipulator
Khoa Dang Nguyen,하철근,Truong Quang Dinh,James Marco 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.3
A 3-RRR parallel manipulator has been well-known as a closed-loop kinematic chain mechanism in which the end-effector generally a moving platform is connected to the base by several independent actuators. Performance of the robot is decided by performances of the component actuators which are independently driven by tracking controllers without acknowledging information from each other. The platform performance is degraded if any actuator could not be driven well. Therefore, this paper aims to develop an advanced synchronization (SYNC) controller for position tracking of a 3-RRR parallel robot using three DC motor-driven actuators. The proposed control scheme consists of three sliding mode controllers (SMC) to drive the actuators and a supervisory controller named PID-neural network controller (PIDNNC) to compensate the synchronization errors due to system nonlinearities, uncertainties and external disturbances. A Lyapunov stability condition is added to the PIDNNC training mechanism to ensure the robust tracking performance of the manipulator. Numerical simulations have been performed under different working conditions to demonstrate the effectiveness of the suggested control approach.
김순욱,Nguyen Tri Khoa,Doan Van Thuan,Dinh Khoi Dang,허승현,김의정,한성홍 한국화학공학회 2017 Korean Journal of Chemical Engineering Vol.34 No.2
ZnO nanoparticle-assembled hollow spheres (raspberry-like) and elliptical nanorods (rice-like) were synthesized via a facile polyol process. Employing ethylene glycol as a polyol led to a ZnO nanoparticle-assembled hollow sphere structure, while diethylene glycol resulted in an elliptical nanorod structure. The ZnO hollow spheres had a higher Brunauer-Emmett-Teller (BET) surface area, better dye adsorption, more incident light trapping, and lower defect density than the ZnO elliptical nanorods. The ZnO hollow sphere-based dye-sensitized solar cells (DSSCs) exhibited a three-times higher current density than the ZnO elliptical nanorod-based DSSCs.
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.