Vu T.V.,Hanoi University of Science and Technology
International Journal of Multiphase Flow | Year: 2017
We present numerical simulations of solidification in a vertical cylindrical annulus with temporal evolution of three interfaces, i.e., solid–liquid, solid–gas, and liquid–gas, and with the presence of natural convection. The numerical technique used is an axisymmetric front-tracking/finite difference method in which the interface separating two phases is represented by connected elements moving on a stationary grid. The governing Navier–Stokes and energy equations are solved in the entire domain with the no-slip and isothermal boundary conditions treated by interpolation techniques. A simple tri-junction condition is included due to the presence of three phases. Effects of various dimensionless parameters such as the Prandtl number Pr, the Stefan number St, the Rayleigh number Ra, the Weber number We, the dimensionless initial temperature of the liquid θ0, and the density ratio of the solid to liquid phases ρsl are investigated. The effect of the tri-junction in terms of the growth angle ϕgr is also considered. Numerical results show that the shape of the solidified phase is strongly affected by ρsl and ϕgr. Volume expansion (ρsl < 1.0) produces a U-shaped top surface while shrinkage (ρsl > 1.0) forms a cavity near the outer wall of the annulus. An increase in ϕgr results in an increase in its slope near the outer wall. Without volume change (ρsl = 1.0), the top surface of the solidified phase becomes more curved with an increase in Pr or We. In contrast, varying St in the range of 0.01–1.0, Ra in the range of 103–106 or θ0 in the range of 1.0–2.0 has only a very minor effect on the top surface. Concerning the circulation flows induced by natural convection, the remarkable effects are yielded by variation of Ra and θ0: increasing Ra or θ0 results in an increase in the strength and the number of circulations. The circulations along with the interfacial tension force are the sources of the top front and solidification interface deformation. In addition, the effects of these parameters on the solidification rate are also investigated. © 2017 Elsevier Ltd
Quyen N.X.,Hanoi University of Science and Technology
Physical Communication | Year: 2017
This paper presents the design of a multi-carrier correlation delay-shift keying (MC-CDSK) system for the operation in wireless environments. In the proposed system, the sum of a chaotic sequence and it delayed version is considered to be a reference sequence and transmitted through a predefined subcarrier. The input data is divided into multiple pairs of bit sub-sequences, where the first and second ones of each pair are spread in the frequency domain by directly multiplying with the chaotic sequence and the delayed version, respectively. The sum of two resulting signals for each pair is then transmitted on a corresponding subcarrier. In the receiving side, the reference sequence retrieved from the predefined subcarrier and the signal retrieved from each of the remaining subcarriers are correlated with the delayed version of the other ones to recover the corresponding bit sub-sequence pair. The recovered pairs are combined to an output data. Schemes for the transmitter and receiver are designed and their operation over a multipath Rayleigh fading channel is described. The system performance is evaluated via theoretical analysis and then verified by numerical simulation. Our findings show that MC-CDSK system can improve communication features, i.e., bit error rate (BER) performance, energy and spectrum efficiency compared to those of the conventional CDSK. © 2017 Elsevier B.V.
Le M.-Q.,Hanoi University of Science and Technology
Computational Materials Science | Year: 2017
The present work investigates through reactive molecular dynamics simulations the mechanical properties of penta-graphene (PG), hydrogenated PG (HPG), and penta-CN2 at 300, 500, 700, and 900 K. Results reveal the higher temperature, the easier and faster transition under tension of PG to a structure, which is similar to a defective graphene. When increasing temperature from 300 to 900 K, the Young's modulus of PG reduces by 10%, but its yield stress (maximal tensile stress in the first stage before transition) and yield strain decrease considerably. The yield strain and yield in-plane stress of PG are about 10.75% and 3%; and 22.4 N/m and 7.9 N/m at 300 and 900 K, respectively. In the second stage with transition, the axial tensile stress increases, reaches a maximal value then decreases slowly. The maximal in-plane stress of PG in the second stage falls within 17–20 N/m when temperature varies in the range of 300–900 K, and the strain at this maximal stress is 40.2, 35.0, 35.4 and 35.6% at 300, 500, 700, and 900 K, respectively. The mechanical properties of HPG and penta-CN2 sheets decrease slightly with an increase of temperature. Hydrogenation reduces the Young's modulus of PG by 25–28%, but increases the maximal tensile stress because HPG does not undergo phase transformation under tension, while PG does. Among three examined sheets, the penta-CN2 sheet exhibits the highest Young's modulus, but the lowest tensile strength and fracture strain. At 300 K, the two-dimensional (2D) Young's modulus, 2D tensile strength and strain at tensile strength of HPG and penta-CN2 sheets are 210 and 314 N/m; 28.7 and 14.4 N/m; and 19.6 and 9.6%, respectively. © 2017
Agency: European Commission | Branch: H2020 | Program: CSA | Phase: GALILEO-4-2014 | Award Amount: 1.83M | Year: 2015
The project implements a set of coordinated actions to promote EGNSS technology in South East Asia (SEA), meanwhile supporting the competitiveness of EU enterprises facilitating their contacts with relevant GNSS stakeholders in SEA, a fast growing market of more than 600 million people. Exploiting the facilities offered in Hanoi by the NAVIS Centre - a strategic asset for Europe, setup with FP7 EU funding - European enterprises can increase their competitiveness conducting tests of their products in a challenging multi-GNSS environment, not available in Europe, with hard ionospheric activity conditions. Ten workshops organised in the different ASEAN States promote EGNSS technology and offer contact opportunities with local stakeholders to EU companies/institutions. Three editions of the Asia Oceania Regional Workshop on GNSS, an important event in SEA, are organized in collaboration with JAXA, MGA and other partners. To reach as many interested EU GNSS companies as possible, the project activities and collaboration opportunities offered by the NAVIS Centre are carefully advertised through different channels including clusters, social networks, websites etc. and three events are organized in Europe, possibly as side events of larger ones. So a larger network of long lasting relations between European companies and SEA GNSS stakeholders is built, allowing the NAVIS Centre to keep serving as a focal point for cooperation with Europe and as showcase of EGNSS technology. A competition to attract smart young researchers/entrepreneurs from ASEAN States to develop EGNSS-based business ideas/applications is also organized. The prize consists in a six-month incubation period in Europe to further implement the idea. Capacity building actions complete the project: they target SEA researchers/technicians with the aim to prepare a generation of SEA experts familiar with European technology, habits and culture and ready to support European industries willing to operate in SEA.
News Article | December 8, 2016
Rigaku Oxford Diffraction is pleased to report its sponsorship of the 14th Conference of the Asian Crystallography Association (AsCA 2016). The conference, held December 4-7, 2016 at the Hanoi University of Science and Technology, was established to cover all major aspects of crystallography-related disciplines, including synchrotron/neutron, structural biology, chemical crystallography, materials and polymer science, crystal growth/crystallization, electron microscopy, and informatics. Rigaku Oxford Diffraction, representing its diverse lines of single crystal X-ray diffraction (XRD) instrumentation, was a key sponsor of the event and conducted informative presentations on a variety of topics related single crystal structure determination. ROD was formed as the global single crystal business unit of Rigaku Corporation after the acquisition of the former Oxford Diffraction organization from Agilent Technologies in 2015. ROD is a leader in the field of single crystal analysis, both in the field of chemical crystallography as well as well as macromolecular crystallography. Formed in 1951, Rigaku Corporation is a leading analytical instrumentation company based out of Tokyo, Japan About Rigaku Since its inception in Japan in 1951, Rigaku has been at the forefront of analytical and industrial instrumentation technology. Rigaku and its subsidiaries form a global group focused on general-purpose analytical instrumentation and the life sciences. With hundreds of major innovations to their credit, Rigaku companies are world leaders in X-ray spectrometry, diffraction, and optics, as well as small molecule and protein crystallography and semiconductor metrology. Today, Rigaku employs over 1,400 people in the manufacturing and support of its analytical equipment, which is used in more than 90 countries around the world supporting research, development, and quality assurance activities. Throughout the world, Rigaku continuously promotes partnerships, dialog, and innovation within the global scientific and industrial communities.
Nguyen D.H.,Hanoi University of Science and Technology |
Banjerdpongchai D.,Chulalongkorn University
Automatica | Year: 2011
In this paper, we present a new robust iterative learning control (ILC) design for a class of linear systems in the presence of time-varying parametric uncertainties and additive input/output disturbances. The system model is described by the Markov matrix as an affine function of parametric uncertainties. The robust ILC design is formulated as a minmax problem using a quadratic performance criterion subject to constraints of the control input update. Then, we propose a novel methodology to find a suboptimal solution of the minmax optimization problem. First, we derive an upper bound of the worst-case performance. As a result, the minmax problem is relaxed to become a minimization problem in the form of a quadratic program. Next, the robust ILC design is cast into a convex optimization over linear matrix inequalities (LMIs) which can be easily solved using off-the-shelf optimization solvers. The convergences of the control input and the error are proved. Finally, the robust ILC algorithm is applied to a physical model of a flexible link. The simulation results reveal the effectiveness of the proposed algorithm. © 2011 Elsevier Ltd. All rights reserved.
Le M.-Q.,Hanoi University of Science and Technology
International Journal of Solids and Structures | Year: 2011
It was illustrated by the author in the previous work that combinations between material properties and indentation parameters can be used as mixed parameters in dimensionless functions to capture the indentation response of materials to single and dual sharp indenters. These issues are further extended in the present study. A parametric finite element analysis was performed to investigate the conical indentation response of elasto-plastic solids. Frictional effects are studied. Conical indenters of half-included angles from 50° to 88° are considered to examine several fundamental features of instrumented sharp indentation within the frame work of limit analysis. Regarding dimensional analysis, it is found that a Taylor series expansion according to the elastic indentation work-total indentation work ratio W e/Wt can be used to improve dimensionless functions. Within this context, a new set of dimensionless functions is explicitly constructed for hardness and indentation parameters of single and dual indenters. Based on formulated functions, a reverse analysis with dual sharp indenters, which was previously proposed by the author, is improved to extract mechanical properties of materials. © 2011 Elsevier Ltd. All rights reserved.
Van Khang N.,Hanoi University of Science and Technology
Mechanics Research Communications | Year: 2011
The automatic derivation of motion equations is an important problem of multibody system dynamics. Firstly, an overview of the matrix calculus related to Kronecker product of two matrices is presented. A new matrix form of Lagrangian equations with multipliers for constrained multibody systems is then developed to demonstrate the usefulness of Kronecker product of two matrices in the study of dynamics of multibody systems. Finally, the equations of motion of mechanisms are derived using the proposed matrix form of Lagrangian equations as application examples. © 2011 Elsevier Ltd.
Le M.-Q.,Hanoi University of Science and Technology
Journal of Computational and Theoretical Nanoscience | Year: 2014
Molecular dynamics simulations were carried out to investigate the tensile mechanical behavior of hexagonal aluminum nitride (AlN), boron nitride (BN), gallium nitride (GaN), indium nitride (InN), and silicon carbide (SiC) monolayer sheets. The Tersoff and Tersoff-like potentials are used to model the interatomic interaction. Every sheet contains 4032 atoms. Stress-strain curves are established in the armchair and zigzag directions for uniaxial tensile response. Compared to graphene, hexagonal BN, SiC, AlN, InN, and GaN monolayer sheets exhibit approximately 77%, 53%, 41%, 27%, and 25% in Young's modulus; and 86%, 49%, 36%, 22% and 26% in fracture stress in the zigzag direction, respectively. Fracture strains appear about 19.5-22.8% and 15.5-17.7% in the zigzag and armchair directions, respectively. It is found that fracture stress-Young's modulus ratios of these 5 sheets and graphene are fairly different. Copyright © 2014 American Scientific Publishers.
Le M.-Q.,Hanoi University of Science and Technology
Mechanics of Materials | Year: 2012
It was illustrated by the author in the previous work that combinations between material properties and indentation parameters can be used as mixed parameters in dimensionless functions to capture the sharp indentation response of materials. These issues are further extended for spherical indentation in the present study. Instrumented spherical indentation was performed by a parametric finite element analysis for a wide range of materials with maximum indentation depth-indenter radius ratios rising from 0.01 to 0.3 to investigate several fundamental features within the frame work of limit analysis. Frictional effects are taken into account. Regarding dimensional analyses and using a Taylor series expansion, a new set of dimensionless functions is constructed for spherical indentation parameters and hardness associated to a 70.3° conical indenter. Based on formulated functions, a reverse analysis procedure is suggested to extract material properties and hardness from spherical indentation force-depth curves with respect to two different indentation depth-indenter radius ratios. Effects of indenter compliance on indentation parameters and reverse results are considered. The accuracy of the proposed method is studied and discussed by carrying out reverse and sensitivity analyses for 22 representative materials with rigid and deformable indenters. © 2011 Elsevier Ltd. All rights reserved.