Phương Nhi

Nguyen, Thoi, T. Nguyen, Xuan H. Tran, Nguyen C. The paper presents an adaptive analysis within the framework of the node-based smoothed finite element method (NS-FEM) using triangular elements. An error indicator based on the recovery strain is used and shown to be asymptotically exact by an effectivity index and numerical results. A simple refinement strategy using the newest node bisection is briefly presented. The numerical results of some benchmark problems show that the present adaptive procedure can accurately catch the appearance of the steep gradient of stresses and the occurrence of refinement is concentrated properly. The energy error norms of adaptive models for both NS-FEM and FEM obtain higher convergence rate compared with the uniformly refined models, but the results of NS-FEM are better and achieve higher convergence rate than those of FEM. The effectivity index of NS-FEM is also closer and approaches to unity faster than that of FEM. The upper bound property in the ...

Dinh, N T, T.A. Nghia Vallet, G. This paper concerns a closedness condition called (CC) involving a convex function and a convex constrained system. This type of condition has played an important role in the study of convex optimization problems. Our aim is to establish several characterizations of this condition and to apply them to study problems of minimizing a DC function under a cone-convex constraint and a set constraint. First, we establish several so-called 'Toland-Fenchel-Lagrange' duality theorems. As consequences, various versions of generalized Farkas lemmas in dual forms for systems involving convex and DC functions are derived. Then, we establish optimality conditions for DC problem under convex constraints. Optimality conditions for convex problems and problems of maximizing a convex function under convex constraints are given as well. Most of the results are established under the (CC) condition. This article serves as a link between several corres...

Nguyen, Huy Tuan Bui, Thanh Duy Nguyen, Dang Minh Vo, Anh Khoa We consider an inverse heat conduction problem for the non-linear heat equation which appears in some applied subjects. The problem is severely ill-posed. Using some modified regularization method, we establish a regularized solution which gives error estimate of Holder type for all t is an element of [0, T]. Some numerical examples show that the computational effect of these methods are all satisfactory. Chi tiết xin mời tham khảo tại http://repository.vnu.edu.vn/handle/VNU_123/29312   Title:  Holder stability for a class of initial inverse nonlinear heat problem in multiple dimension Authors:  Nguyen, Huy Tuan Bui, Thanh Duy Nguyen, Dang Minh Vo, Anh Khoa) Keywords:  Backward heat problem;Nonlinearly ill-posed problem;Quasi-boundary value methods;Quasi-reversibility methods Issue Date:  2015 Publisher:  ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS Citation:...

Nguyen, Van Hieu We use the Logunov-Tavkhelidze quasipotential approach to study some processes of quantum chromo-dynamics at finite densities and temperatures. The dynamic equation for the color superconductivity is derived. We discuss the spontaneous breaking of the chiral, flavor, and color symmetries and also the possibility of constructing a field theory of the composite three-quark systems. Chi tiết xin mời tham khảo tại http://repository.vnu.edu.vn/handle/VNU_123/31416   Title:  Quasipotential approach to quantum chromodynamics Authors:  Nguyen, Van Hieu Keywords:  Flavor symmetry;Three-quark systems;quantum chromodynamics;Color symmetry;Chiral symmetry Issue Date:  2002 Publisher:  CONSULTANTS BUREAU, 233 SPRING ST, NEW YORK, NY 10013 USA Citation:  ISIKNOWLEDGE Description:  THEORETICAL AND MATHEMATICAL PHYSICS Volume: 132 Issue: 2 Pages: 1144-1147 ; TNS06516 URI:  http://repository.vnu.edu.vn/handle/VNU_123...

N.D. The N. Chau N.V. Vuong N.H. Quyen The formation of special nanostructure, cellular structure, in Nd4.5Fe73.8B18.5Cr0.5Co1.5Nb1Cu0.2 nanocomposite magnet has been observed by means of SEM for the first time. Ultrafine structure of cellules with thickness of 20-25 nm and length in range of 200-300 nm leads to high shape anisotropy of the materials. Therefore, high hard magnetic properties were obtained with (BH)(max) up to 17.3 MG Oe in ribbons with very high remanence of 13.5 kG. The role of Cr and Co in the formation and refinement of cellular structure is proposed. Effect of heat treatment on hard magnetic properties is discussed in detail.   Chi tiết xin mời tham khảo tại http://repository.vnu.edu.vn/handle/VNU_123/31661 Title:  High hard magnetic properties and cellular structure of nanocomposite magnet Nd4.5Fe73.8B18.5Cr0.5Co1.5Nb1Cu0.2 Authors:  N.D. The N. Chau N.V. Vuong N.H. Quyen Keywords:  Amorphous alloys;Nanocrystalline alloys;Ex...

Nguyen, Anh Tuan Nguyen, Chau Nguyen, Hoang Luong High coercivity was obtained in Co–Cu granular films, RF sputtered on Si(10 0) substrates, when the Co content is less than about 40 at% and annealed at high temperatures. Perpendicular anisotropy was observed in the Co-rich films, where the Co content is not less than about 40 at% atom. The reasons for the high coercivity and the perpendicular anisotropy in these Co–Cu films are discussed Chi tiết xin mời tham khảo tại http://repository.vnu.edu.vn/handle/VNU_123/31843   Title:  High coercivity and perpendicular anisotropy in Co-Cu granular films Authors:  Nguyen, Anh Tuan Nguyen, Chau Nguyen, Hoang Luong Keywords:  Granular films;Superparamagnetic;High coercivity;Perpendicular anisotropy Issue Date:  2003 Publisher:  ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS Citation:  ISIKNOWLEDGE Description:  TNS07865 ; PHYSICA B-CONDENSED MATTER Volume: 327 Issue: 2-4 ...

Tran Kim Anh Paul Benalloul Charles Barthou Lam Thi Kieu Giang Nguyen Vu Le Quoc Minh Luminescence, energy transfer, and upconversion mechanisms of nanophosphors (Y(2)O(3) : Eu(3+), Tb(3+), Y(2)O(3) : Tm(3+), Y(2)O(3) : Er(3+), Yb(3+)) both in particle and colloidal forms were studied. The structure, phase, and morphology of the nanopowders and nanocolloidal media were determined by high-resolution TEM and X-ray diffraction. It was shown that the obtained nanoparticles have a round-spherical shape with average size in the range of 4 to 20 nm. Energy transfer was observed for Y(2)O(3) : Eu(3+), Tb(3+) colloidal and powders, upconversion transitions were observed for both Y(2)O(3) : Er(3+) and Y(2)O(3) : Er(3+), Yb(3+) nanophosphors. The dependence of photoluminescence (PL) spectra and decay times on doping concentration has been investigated. The infrared to visible conversion of emission in Y(2)O(3) : Er(3+), Yb(3+) system was analyzed and discussed aiming to be applied...