Papers by Nguyen Kim Tuan
The paper is a continuation of the works [17] of Vu and Shum, [18] and [19] of Vu and Hoa. In [17... more The paper is a continuation of the works [17] of Vu and Shum, [18] and [19] of Vu and Hoa. In [17], Vu and Shum classified all the MD5-algebras having commutative derived ideals. In [18], Vu and Hoa considered foliations formed by the maximal dimensional K-orbits (for short, MD5-foliations) of connected MD5-groups such that their Lie algebras have 4-dimensional commutative derived ideals and gave a topological classification of the considered foliations. In [19], Vu and Hoa characterized the Connes' C*-algebras of some MD5-foliations considered in [18] by the method of K-functors. In this paper, we study K-theory for the leaf space of all MD5-foliations which are classified in [18] and characterize the Connes' C*-algebras of them by the method of K-functors.
Japan Society of Civil Engineers, May 15, 2020
Meeting Abstracts of the Physical Society of Japan (Nihon Butsuri Gakkai koen gaiyoshu), 2011
Scientiae mathematicae Japonicae, 2010
In this paper we constructed separately the algebras generated by the idempotents operators, and ... more In this paper we constructed separately the algebras generated by the idempotents operators, and by nilpotents operators, and prove the isomorphic theorems between original algebras and algebras of symbols. In particular, Theorems 2.1, 2.2 prove that an operator is generalized invertible if and only if so its symbol is.
The study was conducted to analyze the factors affecting learners’ satisfaction towards quality o... more The study was conducted to analyze the factors affecting learners’ satisfaction towards quality of English Certification Training services in Vietnam. Qualitative and quantitative research methods in combination were selected to survey 566 learners using 47 observed variables to determine influential factors of the service quality. The study results revealed 5 factorial groups that proved to have impact on learners’ satisfaction: (1) Competence, (2) Tangibles, (3) Empathy, (4) Responsiveness, and (5) Reliability. The objects of the findings are as follows: firstly, to identify the factors that affect learners’ satisfaction towards service quality of English Certification Training; secondly, to determine the order or ranking of factors explored from most to least influential level; and thirdly, to propose solutions for enhancing learners’ satisfaction toward the service quality in the future.
Applicable Analysis, 2021
Miskolc Mathematical Notes, 2013
We study the backward parabolic problem for a nonlinear parabolic equation of the form u t C Au.t... more We study the backward parabolic problem for a nonlinear parabolic equation of the form u t C Au.t/ D f .t; u.t//; u.T / D ', where A is a positive self-adjoint unbounded operator and f is a Lipschitz function. The problem is ill-posed, in the sense that if the solution does exist, it will not depend continuously on the data. To regularize the problem, we use the quasiboundary method and the quasi-reversibility method to establish a modified problem. We present approximated solutions that depend on a small parameter > 0 and give error estimates for our regularization.
International Journal of Entrepreneurship and Innovation Management, 2017
Lean manufacturing (LM), often simply named as 'lean', plays an important role in enterpr... more Lean manufacturing (LM), often simply named as 'lean', plays an important role in enterprises to eliminate waste, increase productivity and efficiency. Visual management (VM) is one of the most efficient and widely used tools and techniques in LM in addition to other techniques like 5S, Kaizen, just-in-time, etc. Lean has been introduced in Vietnam for more than ten years, but few enterprises have applied and attained significant achievement. The purpose of this paper is to analyse the barriers to VM implementation in small- and medium-sized enterprise (SMEs) in Vietnam. In this study, in-depth semi-structured interviews, surveys, plant visit (factory tour) and, in some cases, observed managers' statements and conversations with blue-collar workers are used to collect relevant data. Based on the results, a VM model which consists of five main factors including human mindset, employee participation, board of management's long-term commitment, training program, and reward/punishment policy, is proposed for further development of LM in SMEs in Vietnam.
The Journal of general virology, Jan 4, 2017
Rural farming communities in northern Vietnam do not routinely practice vaccination for influenza... more Rural farming communities in northern Vietnam do not routinely practice vaccination for influenza A viruses (IAV) for either humans or poultry, which enables us to study transmission intensity via seroepidemiology. Using samples from a longitudinal cohort of farming households, we determined the number of symptomatic and asymptomatic human infections for seasonal IAV and avian A/H9 over 2 years. As expected, we detected virologically confirmed acute cases of seasonal IAV in humans, as well as large numbers of subclinical seroconversions to A/H1pdm [55/265 (21 %)], A/H3 [95/265 (36 %)] and A/H9 [24/265 (9 %)]. Five of the A/H9 human seroconverters likely represented true infections rather than heterosubtypic immunity, because the individuals seroconverted solely to A/H9. Among co-located poultry, we found significantly higher seroprevalance for A/H5 compared to A/H9 in both chickens and ducks [for northern study sites overall, 337/1105 (30.5 %) seropositive for A/H5 and 123/1105 (11....
MATERIALS TRANSACTIONS, 2016
Several forms of graphene-based magnetic materials have been investigated via density-functional ... more Several forms of graphene-based magnetic materials have been investigated via density-functional theory utilizing dispersion correction and full geometry optimization. Our calculated results show that the perinaphthenyl radical (R 1) has a spin of 1/2. However, in its [R 1 ] 2 dimer structure, the net spin becomes zero due to an antiferromagnetic spin-exchange between radicals. To avoid antiferromagnetic spin-exchange of identical face-to-face radicals, the alternating stack of composition R 1 /D 25 /R 1 (with D 25 = graphene-based diamagnetic molecule C 34 H 16) has been designed and investigated. As expected, our calculated results con rm that the alternating stack R 1 /D 25 /R 1 has a ferromagnetic spin-exchange between two R 1 radicals with the spin-exchange coupling of J/k B = 277 K, and the spin moment of m = 2 μ B (Bohr magneton unit). In order to explore ways to tailor spin-exchange coupling in stacks, ve other R 1 /D 25 /R 1-based alternating stacks with different ligand con gurations of R 1 have been designed and investigated. Interestingly, ferromagnetic spin-exchange in stacks can be enhanced by substituting ligands having a weak electron af nity for H atoms of a R 1 molecule, while it can be weakened by substituting ligands having high electron af nity for H atoms of a R 1 radical. These results can be explained in terms of the competitive hybridization between the HOMO (highest occupied molecular orbital) of radicals and the HOMO and LUMO (lowest unoccupied molecular orbital) of diamagnetic molecules. These results would give some indication for how the spin-exchange coupling in graphene-based alternating stacks can be tailored.
In this paper, our aim is to study a numerical method for an ultraparabolic equation with nonline... more In this paper, our aim is to study a numerical method for an ultraparabolic equation with nonlinear source function. Mathematically, the bibliography on initial-boundary value problems for ultraparabolic equations is not extensive although the problems have many applications related to option pricing, multi-parameter Brownian motion, population dynamics and so forth. In this work, we present the approximate solution by virtue of finite difference scheme and Fourier series. For the linear case, we give the approximate solution and obtain a stability result. For the nonlinear case, we use an iterative scheme by linear approximation to get the approximate solution and obtain error estimates. Some numerical examples are given to demonstrate the efficiency of the method.
Journal of Computational and Applied Mathematics, 2017
In this paper, we rigorously investigate the truncation method for the Cauchy problem of Helmholt... more In this paper, we rigorously investigate the truncation method for the Cauchy problem of Helmholtz equations which is widely used to model propagation phenomena in physical applications. The method is a well-known approach to the regularization of several types of ill-posed problems, including the model postulated by Regińska and Regiński [14]. Under certain specific assumptions, we examine the ill-posedness of the non-homogeneous problem by exploring the representation of solutions based on Fourier mode. Then the so-called regularized solution is established with respect to a frequency bounded by an appropriate regularization parameter. Furthermore, we provide a short analysis of the nonlinear forcing term. The main results show the stability as well as the strong convergence confirmed by the error estimates in L 2-norm of such regularized solutions. Besides, the regularization parameters are formulated properly. Finally, some illustrative examples are provided to corroborate our qualitative analysis.
Applied Mathematics and Computation, Mar 31, 2015
Journal of Surface Analysis, 2011
We have measured optical second harmonic (SH) intensity from Pt nanowires with modified ellipsoid... more We have measured optical second harmonic (SH) intensity from Pt nanowires with modified ellipsoidal cross sections on the MgO(110) faceted template. The observed SH intensity patterns as a function of the sample rotation angle φ around the surface normal were characterized by the effective nonlinear susceptibility arising from C s symmetry of the Pt nanowires. The effective nonlinear susceptibility element χ 222 was observed dominantly with the suffix 2 representing the [11-0] direction of the MgO substrate. Other nonlinear susceptibility elements were also detected and their origins are discussed.
We consider the following problem u xx + u yy = 0, (x, y) ∈ (0, π) × (0, 1) u(0... more We consider the following problem u xx + u yy = 0, (x, y) ∈ (0, π) × (0, 1) u(0, y) = u(π, y) = 0, y ∈ (0, 1) u y (x, 0) = g(x), 0 < x < π u(x, 0) = ϕ(x), 0 < x < π The problem is shown to be ill-posed, as the solution exhibits unstable dependence on the given data functions. Using the new method, we regularize of problem and obtain some new results. Some numerical examples are given to illuminate the effect of our methods.
In this paper, we consider an inverse problem to determine a source term in a parabolic equation,... more In this paper, we consider an inverse problem to determine a source term in a parabolic equation, where the data are obtained at a certain time. In general, this problem is ill-posed, therefore the Tikhonov regularization method is proposed to solve the problem. In the theoretical results, a priori error estimate between the exact solution and its regularized solution is obtained. We also propose both methods, a priori and a posteriori parameter choice rules. In addition, the proposed methods have been verified by numerical experiments to estimate the errors between the regularized solutions and exact solutions. Eventually, from the numerical results it shows that the a posteriori parameter choice rule method gives a better the convergence speed in comparison with the a priori parameter choice rule method in some specific applications.
International Journal of Mechanical Engineering and Applications, Jan 14, 2015
The aim of our paper is to study the effects of roll motion on a transverse stability of a small ... more The aim of our paper is to study the effects of roll motion on a transverse stability of a small boat. Roll frequency will be calculated and analyzed for reducing motion sickness based on stabilit solution of ship roll motion will be also investigated in our paper.
Mathematical Communications
We consider a nonlinear backward heat conduction problem in a strip. The problem is ill-posed in ... more We consider a nonlinear backward heat conduction problem in a strip. The problem is ill-posed in the sense that the solution (if it exists) does not depend continuously on the data. We shall use a modified integral equation method to regularize the nonlinear problem. The error estimates of Hölder type of the regularized solutions are obtained.
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Papers by Nguyen Kim Tuan