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Communications in Theoretical Physics 2019年第8期71卷 947-954页

作者： nguyen Huy Bang Le nguyen Mai Anh nguyen Tien Dung Le Van Doai Vinh University 182 Le Duan Street Vinh City Vietnam Nong Lam University Ho Chi Minh City Vietnam (Received March 21 2019revised manuscript

We present a comparative study of the control of group velocity in three-level atomic systems including Λ-, Ladder-, and V-types via spontaneously generated coherence(SGC) and relative phase of laser *** the steady regime, expressions of group index are derived as an analytical function of controllable parameters related to SGC and relative *** is shown that the group velocity can be further slowed down or speeded up under SGC in which modifications of group velocity due to the SGC in Λ-and V-systems are stronger than that in *** particular, when interference strength of SGC p increases from 0.7 to 1.0, the light propagation is switched from superluminal to subluminal modes(for Λ-and Ladder-systems) or from subluminal to superluminal modes(for Vsystem).In the presence of relative phase, the group velocity changes between subluminal and superluminal modes with a period of 2π.In resonant region, the largest positive value of group index reaches at the relative phase φ=π while the largest negative value of group index reaches at φ= 0 and 2π for the Λ-and Ladder-systems, otherwise, for the V-system the largest positive group index occurs at φ= 0 and 2π, and the largest negative group index occurs at φ=π.

关键词： electromagnetically induced transparency spontaneously generated coherence group velocity

Scouring of a granular bed by dam break: Experimental study and numerical simulation by a VOF-LPT coupling

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International Journal of Sediment Research 2023年第3期38卷 432-445页

作者： Quyen Thi Le nguyen Viet Dung nguyen Patrice Coorevits EPROAD Research Unit University of Picardie Jules Verne IUT of Aisne Hanoi University of Civil Engineering

The first part of the research reported here consists of an experimental campaign to study the scouring of a granular bed(glass beads, sand) induced by a dam break in an open channel. Two configurations are considered: with and without cylinders. In the second part of this study, the volume of fluid method coupled with the shear stress transport turbulent model and the lagrangian particle tracking method is used to simulate the local scour processes. The four-way coupling is realized by considering the drag force and collisions between particles. Using a vortex map and velocity profiles, the flow dynamics and scour pattern can be studied. The current research also focuses on the profiles of the erodible particle bed and the sediment transport rate to study the effects of a cylinder on local scour. The presence of the cylinder increases the experimental erosion depth by up to 42%. It was found that for relatively close particle diameters(2 and 3 mm), a granular bed with larger porosity(larger diameter) erodes the *** and numerically it was found that the center of the granular bed experiences more erosion compared to the channel sides. In the last part of the research, comparisons between the numerical results and the experimental data allowed risk areas to be identified and the roles of porosity,sediment density, and flow dynamics on erosion to be identified.

关键词： Volume of fluid Lagrangian particle tracking Scour Granular bed Cylinder Dam break

Influence of Input Factors on Surface Roughness and Material Removal Speed when Wire-EDM a Hardened SKD11 Steel Curve Profile

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Journal of Environmental Science and Engineering(B) 2023年第5期12卷 220-229页

作者： Tran Quoc hung nguyen Van Trang Ha Noi University of Industry Bac Tu Liem District 143315Ha Noi cityVietnam Thai nguyen University of Technology Thai Nguyen city 251750Vietnam

The goal of this research is to identify the best set of process machining parameters for wire-EDM(Electrical Discharge Machining)cutting of hardened SKD11 steel when machining a curve *** multi-objective function includes reducing surface roughness and increasing MRR(Material Removal Rate).The optimization process is prepared by using Taguchi method coupled Grey Relational *** obtained results revealed that Toff has the greatest influence on the average grey value(48.30%),followed by the influence of WF(Wire Feed,15.99%),VM(Cutting Voltage,9.33%),SV(Server Voltage,5.05%),Ton(Pulse on Time,1.81%),while SPD(Cutting Speed)has a negligible effect(0.89%).Moreover,using the optimal set of machining parameters generates in surface roughness of 1.25399mm and MRR of 26.5562 mm^(2)/*** verification experiment and Anderson-Darling method demonstrate the validity of the proposed model,which can be utilized for estimating surface roughness and MRR.

关键词： Wire Electrical Discharge Machining wire-EDM surface roughness Material Removal Speed SKD11.

An Integrated and Comprehensive Fuzzy Multi-Criteria Model for Electronic Wallet Selection

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Computers, Materials & Continua 2023年第1期74卷 2279-2301页

作者： Phuoc Van nguyen Faculty of Business Administration Posts and Telecommunications Institute of Technology(PTIT)Ho Chi Minh City700000Vietnam

Electronic wallet(E-wallet),which combines software,hardware,and human interaction,is a modern platform for electronic *** services managers can create more effective strategies for advancing existing positions by evaluating the success of e-wallet *** objective of this research is to create an integrated model for assessing E-wallet services using the Fuzzy Analytic Hierarchy Process(FAHP)in conjunction with a technique for extent analysis and the ARAS approach(Additive Ratio Assessment).In this study,E-wallet service providers are ranked and evaluated using the ARAS approach and the FAHP priority *** addition,a case study from Vietnam illustrates how the methodology is *** data shows that perceived usefulness,perceived usability,perceived simplicity of use,and perceived threat have the least impact on how acceptable an Ewallet *** a result,the suggested model improves the efficiency of E-wallet service operations and assists in overcoming the challenges associated with the evaluation of E-wallet *** case finding demonstrates that the suggested model is a reliable and useful tool for making decisions when assessing E-wallet service providers functioning in a complex and changing environment.

关键词： Financial services provider E-wallet adoption fuzzy AHP ARAS

Negative Index Materials and Their Applications:Recent Mathematics Progress(Dedicated to Ham Brezis for his 70th birthday with esteem)

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Chinese Annals of Mathematics,Series B 2017年第2期38卷 601-628页

作者： Hoai-Minh nguyen EPFL SB MATHAA CAMA Station 8CH-1015 LausanneSwitzerland

Negative index materials are artificial structures whose refractive index has negative value over some frequency range. These materials were first investigated theoretically by Veselago in 1946 and were confirmed experimentally by Shelby, Smith, and Schultz in2001. Mathematically, the study of negative index materials faces two difficulties. Firstly,the equations describing the phenomenon have sign changing coefficients, hence the ellipticity and the compactness are lost in general. Secondly, the localized resonance, i.e.,the field explodes in some regions and remains bounded in some others as the loss goes to 0, might appear. In this survey, the author discusses recent mathematics progress in understanding properties of negative index materials and their applications. The topics are reflecting complementary media, superlensing and cloaking by using complementary media, cloaking a source via anomalous localized resonance, the limiting absorption principle and the well-posedness of the Helmholtz equation with sign changing coefficients.

关键词： Negative index materials, Localized resonance, Cloaking, Superlensing

Asymptotic Expansions of Backward Equations for Two-time-scale Markov Chains in Continuous Time

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Acta Mathematicae Applicatae Sinica 2009年第3期25卷 457-476页

作者： Dung Tien nguyen Department of Mathematics Wayne State University

This work develops asymptotic expansions for solutions of systems of backward equations of time- inhomogeneous Maxkov chains in continuous time. Owing to the rapid progress in technology and the increasing complexity in modeling, the underlying Maxkov chains often have large state spaces, which make the computa- tional tasks ihfeasible. To reduce the complexity, two-time-scale formulations are used. By introducing a small parameter ε〉 0 and using suitable decomposition and aggregation procedures, it is formulated as a singular perturbation problem. Both Markov chains having recurrent states only and Maxkov chains including also tran- sient states are treated. Under certain weak irreducibility and smoothness conditions of the generators, the desired asymptotic expansions axe constructed. Then error bounds are obtained.

关键词： Markov chain backward equation two-time scale asymptotic expansion

ON BOUNDEDNESS PROPERTY OF SINGULAR INTEGRAL OPERATORS ASSOCIATED TO A SCHRODINGER OPERATOR IN A GENERALIZED MORREY SPACE AND APPLICATIONS

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Acta Mathematica Scientia 2020年第5期40卷 1171-1184页

作者： Xuan Truong LE Thanh Nhan nguyen Ngoc Trong nguyen Division of Computational Mathematics and Engineering Institute for Computational ScienceTon Due Thang UniversityHo Chi Minh CityVietnam Faculty of Mathematics and Statistics Ton Due Thang UniversityHo Chi Minh CityVietnam Department of Mathematics Ho Chi Minh City University of EducationHo Chi Minh CityVietnam Department of Primary Education Ho Chi Minh City University of EducationHo Chi Minh CityVietnam

In this paper,we provide the boundedness property of the Riesz transforms associated to the Schrodinger operator■=-Δ+V in a new weighted Morrey space which is the generalized version of many previous Morrey type *** additional potential V considered in this paper is a non-negative function satisfying the suitable reverse Holder's *** results are new and general in many cases of *** an application of the boundedness property of these singular integral operators,we obtain some regularity results of solutions to Schrodinger equations in the new Morrey space.

关键词： weighted Morrey spaces Schodinger operator riesz transforms Regularity estima tes

Non-Negative Adaptive Mechanism-Based Sliding Mode Control for Parallel Manipulators with Uncertainties

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Computers, Materials & Continua 2023年第2期74卷 2771-2787页

作者： Van-Truong nguyen Department of Mechatronics Engineering Hanoi University of IndustryHanoi159999Vietnam

In this paper,a non-negative adaptive mechanism based on an adaptive nonsingular fast terminal sliding mode control strategy is proposed to have finite time and high-speed trajectory tracking for parallel manipulators with the existence of unknown bounded complex uncertainties and external *** proposed approach is a hybrid scheme of the online non-negative adaptive mechanism,tracking differentiator,and nonsingular fast terminal sliding mode control(NFTSMC).Based on the online non-negative adaptive mechanism,the proposed control can remove the assumption that the uncertainties and disturbances must be bounded for the NFTSMC *** proposed controller has several advantages such as simple structure,easy implementation,rapid response,chattering-free,high precision,robustness,singularity avoidance,and finite-time *** all control parameters are online updated via tracking differentiator and non-negative adaptive law,the tracking control performance at high-speed motions can be better in real-time requirement and disturbance rejection ***,simulation results validate the effectiveness of the proposed method.

关键词： Parallel manipulator uncertainties and disturbances nonsingular fast terminal sliding mode control non-negative adaptive mechanism tracking differentiator

A novel finite element formulation for static bending analysis of functionally graded porous sandwich plates

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Frontiers of Structural and Civil Engineering 2022年第12期16卷 1599-1620页

作者： Van Chinh nguyen Trung Thanh TRAN Trung nguyen-THOI Quoc-Hoa PHAM Faculty of Mechanical Engineering Le Quy Don Technical UniversityHanoiVietnam Laboratory for Applied and Industrial Mathematics Institute for Computational Science and Artificial IntelligenceVan Lang UniversityHo Chi Minh CityVietnam Faculty of Mechanical-Electrical and Computer Engineering Van Lang UniversityHo Chi Minh CityVietnam Faculty of Engineering and Technology Nguyen Tat Thanh UniversityHo Chi Minh CityVietnam

This article aims to propose a finite element formulation based on Quasi-3D theory for the static bending analysis of functionally graded porous(FGP)sandwich *** FGP sandwich plates consist of three layers including the bottom skin of homogeneous metal,the top skin of fully ceramic and the FGP core layer with uneven porosity distribution.A quadrilateral(Q4)element with nine degrees of freedom(DOFs)per node is derived and employed in analyzing the static bending response of the plate under uniform and/or sinusoidally distributed *** accuracy of the present finite element formulation is verified by comparing the obtained numerical results with the published results in the ***,some numerical examples are performed to examine the effects of the parameters including power-law index k and porosity coefficient on the static bending response of rectangular FGP sandwich *** addition,a problem with a complicated L-shape model is conducted to illustrate the superiority of the proposed finite element method.

关键词： sandwich plates functionally graded porous static bending Quasi-3D theory Q4 element

NORMAL FAMILY OF MEROMORphiC FUNCTIONS SHARING HOLOMORphiC FUNCTIONS AND THE CONVERSE OF THE BLOCH PRINCIPLE

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Acta Mathematica Scientia 2017年第3期37卷 623-656页

作者： nguyen Van THIN Department of Mathematics Thai Nguyen University of EducationLuong Ngoc Quyen StreetThai Nguyen cityThai NguyenViet Nam

In 1996, C. C. Yang and P. C. Hu [8] showed that： Let f be a transcendental meromorphic function on the complex plane, and a ≠ 0 be a complex number; then assume that n 〉 2, n1,… , nk are nonnegative integers such that n1＋… ＋ nk ≥1; thus fn（f′）n1…（f（k））nk-a has infinitely zeros. The aim of this article is to study the value distribution of differential polynomial, which is an extension of the result of Yang and Hu for small function and all zeros of f having multiplicity at least k ≥2. Namely, we prove that fn（f′）n1…（f（k））nk-a（z） has infinitely zeros, where f is a transcendental meromorphic function on the complex plane whose all zeros have multiplicity at least k≥ 2, and a（z） 0 is a small function of f and n ≥ 2, n1,… ,nk are nonnegative integers satisfying n1＋ …＋ nk ≥1. Using it, we establish some normality criterias for a family of meromorphic functions under a condition where differential polynomials generated by the members of the family share a holomorphic function with zero points. The results of this article are supplement of some problems studied by d. Yunbo and G. Zongsheng [6], and extension of some problems studied X. Wu and Y. Xu [10]. The main result of this article also leads to a counterexample to the converse of Bloeh＇s principle.

关键词： Normal family Nevanlinna theory meromorphic function sharing function differential pOlynomial