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  • Authors: N.N.Hieu; P.N.Chung;  Advisor: -;  Co-Author: - (2021)

    In this paper, the authors investigate the stability and stick-slip motion of a friction-induced vibrating system placed on a belt moving at constant velocity using two-state model with consideration of dwell-time effect. The two-state model can be considered as an extension of the LuGre model because it can capture both Stribeck and dwell-time effects in the case of near-zero relative motion velocity between two surfaces. The previously known Stribeck effect is that the friction force decreases as the relative velocity increases in the near-zero range, while the dwell-time effect exhibits that the friction force increases as two surfaces are kept in contact for a certain time. With new effect of dwell-time, properties of stick-slip motion are explored in detail, including the equil...

  • Authors: Vinh Van, Le; Thi Hinh, Dinh; Thao T. Nguyen; Ha Thi Thanh, Nguyen;  Advisor: -;  Co-Author: - (2022)

    Multiphase Al2O3 samples are simulated using molecular dynamics method. These samples consist of γ-Al2O3 and α-Al2O3 crystals embedded in a disordered phase matrix. The stress–strain curves of these samples show elastic and plastic deformation. Structural analysis indicates that the AlO bond lengths are stretched and the geometries of the AlOx (x = 4, 5, and 6) units are distorted during tensile deformation. AlO bond breakage causes the transformation of AlOx units; AlO4 increases while AlO6 decreases with increasing strain. The γ-Al2O3 and α-Al2O3 crystals transfer into the disordered phase, while a small number of atoms recrystallize under tensile loads. In plastic deformation, large simplexes with radii above 1.958 Å increase rapidly with increasing strains above 0.116, with th...

  • Authors: Duc, Ngoc Nguyen; Ngoc, Duyen Dang; Thi, Thu Huong Tran;  Advisor: -;  Co-Author: - (2022)

    The phenomenon of vehicle rollover usually occurs when the driver suddenly steers at high speed. The centrifugal force will appear and cause the vehicle’s body to tilt. To overcome this situation, the solution of using the stabilizer bar is proposed. The passive stabilizer bar has a simple structure, low cost, and long service life. As a result, it is now a standard on most vehicles. This paper has established a dynamic model to describe a vehicle’s oscillation. As a result of the study, the maximum roll angle of the vehicle was reduced from 9.0° to 8.2° when the stabilizer bar was used. Besides, the minimum value of the vertical force at the wheel reached 485(N) and 1162(N), respectively, corresponding to the two survey cases. The movement trajectory of the vehicle when using the s...

  • Authors: Anh D. Phan; Alessio Zaccone; Vu D. Lam; Katsunori Wakabayashi;  Advisor: -;  Co-Author: - (2021)

    We theoretically investigate high-pressure effects on the atomic dynamics of metallic glasses. The theory predicts compression-induced rejuvenation and the resulting strain hardening that have been recently observed in metallic glasses. Structural relaxation under pressure is mainly governed by local cage dynamics. The external pressure restricts the dynamical constraints and slows down the atomic mobility. In addition, the compression induces a rejuvenated metastable state (local minimum) at a higher energy in the free-energy landscape. Thus, compressed metallic glasses can rejuvenate and the corresponding relaxation is reversible. This behavior leads to strain hardening in mechanical deformation experiments. Theoretical predictions agree well with experiments.

  • Authors: Thanh-Trung Vo; Cuong T. Nguyen; Trung-Kien Nguyen; Van My Nguyen; Thi Lo Vu;  Advisor: -;  Co-Author: - (2021)

    We investigate the impact dynamics of a single wet agglomerate composed of primary spherical particles impacting a flat plane by using three-dimensional discrete element method simulations. The primary particle is assumed to be rigid and interacted with its near-neighboring particles by introducing approximate analytical expressions of capillary cohesion forces and lubrication forces induced from the liquid in addition to their elastic and frictional interactions. The paper analyzes the mechanical strength, the deformation, and the connectivity of wet particle agglomerate during the impact as well as in its early-stage impact and the final-stage deposition. We show that the mechanical strength, deformation, and connectivity of granule strongly depend on the key parameters (the liqui...

  • Authors: Duc-Nam Nguyen; Van-Tuan Nguyen; Ich-Hung Dam; Van-Huong Vu;  Advisor: -;  Co-Author: - (2022)

    A large number of piezoelectric polymers have been studied and applied widely recently and become an attractive topic in both material science and applied engineering fields. Piezoelectric polymers such as Poly(vinyl fluoride) and Poly(γ-benzyl, L-glutamate) fabricated in nanofibers have shown impressive properties in the aspect of low weight, high flexibility and high piezoelectricity. One of the major parameters influencing to the piezoelectricity of electrospun fibers is the orientation. This paper reviews the contribution of fiber orientation to the piezoelectricity properties and the technique to manipulate the orientation. The research group introduces for the first time a fully integrated and compact electrospinning system which is low cost and suitable for both lab-scale and...

  • Authors: Duc, Minh Vua; Mike, Hewitt; Duc, D.Vuc;  Advisor: -;  Co-Author: - (2022)

    In this paper, we present exact methods for solving the Time Dependent Minimum Tour Duration Problem (TD-MTDP) and the Time Dependent Delivery Man Problem (TD-DMP). Both methods are based on a Dynamic Discretization Discovery (DDD) approach for solving the Time Dependent Traveling Salesman Problem with Time Windows (TD-TSPTW). Unlike the TD-TSPTW, these problems involve objective functions that depend in part on the time at which the vehicle departs the depot. As such, optimizing these problems adds a scheduling dimension to the problem. We present multiple enhancements to the DDD method, including enabling it to dynamically determine which waiting opportunities at the depot to model. With an extensive computational study we demonstrate that the resulting methods outperform all know...

  • Authors: Quan Hoang. Vuong; Viet Phuong, La; Minh Hoang, Nguyen;  Advisor: -;  Co-Author: - (2021)

    2014 marked a rising public commitment to universal health coverage in Vietnam to eliminate the financial burden for patients, but there are lots of hindrances. It is evident that patients met difficulties to validate their insurances, so health insurance does not significantly address out-of-pocket payments issues. Furthermore, the unequal geographical distribution of hospitals in Vietnam has created an inequality between non-residing patients and residing patients; the former usually pay more. This calls into question how the validity of healthcare insurance and patient’s residence could be related to patient’s financial status and their satisfaction with health insurance

  • Authors: Thi Kim Quy Ha; Thi Phuong Doan; Ha Thanh Tung Pham; Ngoc Hieu Nguyen; Trong Tuan Nguyen; Thi Buu Hue Bui;  Advisor: -;  Co-Author: - (2021)

    Elaeocarpus hygrophilus Kurz. is a tropical tree that has recently been used for food and medicinal purposes. This study aimed to reveal the phytochemicals and evaluate the anti-influenza viral and neuroprotective effects of different parts of this plant including leaves, stems, fruit peels, and seeds. The study results indicated that the leaf extract was a potential candidate in the inhibition of the influenza viral replication through anti-neuraminidase receptors and attenuation of the glutamate-induced neuronal cell death and cellular oxidative stress. Using molecular networking as well as fragmentation, twenty-six known compounds were dereplicated from the leaves of E. hygrophilus. Molecular docking simulations of target proteins (PDB: 3CL0 and 4CXT) with these predicted compoun...