Thi Tran Co Le, Vietnam
Thi Tran Co Le, Vietnam

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Chen C.-C.A.,National Taiwan University of Science and Technology | Pham Q.-P.,Vinh University
International Journal of Advanced Manufacturing Technology | Year: 2017

Diamond dressing process is critical in conditioning pad surface topography before and after chemical mechanical planarization/polishing (CMP) process for integrated circuit (IC) fabrication. This paper addresses a kinematic model of diamond dressing effect on the profile of pad cutting rate (PCR) with a ring-type diamond dresser through both simulation and experiments. In this kinematic model, the cutting locus distribution, relative velocity of diamond grits on a pad surface, and sliding time have been described as significant factors for non-uniformity of pad surface topography. Moreover, the speed ratio between the diamond dresser and the polishing pad has been investigated with respect to the center distance of the pad and the diamond dresser by the developed method. The model has been verified by experiments of diamond dressing of pad. Experimental results show that the dressing marks and pad cutting rate on the pad surface follow the same trend as simulation results and the final pad surface is obtained as a concave shape. Results of this study can be applied on diamond dressing of pads used in CMP and furthermore can be extended to investigate an optimal diamond dressing process for semiconductor fabrication. © 2017 Springer-Verlag London


Khoa D.X.,Vinh University | Van Doai L.,Vinh University | Son D.H.,Ha Tinh University | Bang N.H.,Vinh University
Journal of the Optical Society of America B: Optical Physics | Year: 2014

We propose to use a five-level cascade system to enhance self-Kerr nonlinearity under an electromagnetically induced transparency (EIT) condition. Using density-matrix theory, an expression of the self-Kerr nonlinear coefficient for a weak probe light is derived. Variations of the self-Kerr coefficient with respect to the frequency and intensity of a strong coupling light are investigated. The Kerr nonlinearity is basically modified and enhanced greatly in the spectral regions Corresponding to EIT transparent windows. Furthermore, the sign, slope, and magnitude of the self-Kerr coefficient can be controlled with the frequency and intensity of the coupling light. Such a controllable Kerr nonlinearity can find interesting applications in optoelectronic devices working with low light intensity at multiple frequencies. © 2014 Optical Society of America.


Nguyen L.A.,University of Warsaw | Cao S.T.,Vinh University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

We formulate query-subquery nets and use them to create the first framework for developing algorithms for evaluating queries to Horn knowledge bases with the properties that: the approach is goal-directed; each subquery is processed only once and each supplement tuple, if desired, is transferred only once; operations are done set-at-a-time; and any control strategy can be used. Our intention is to increase efficiency of query processing by eliminating redundant computation, increasing flexibility and reducing the number of accesses to the secondary storage. The framework forms a generic evaluation method called QSQN. To deal with function symbols, we use a term-depth bound for atoms and substitutions occurring in the computation and propose to use iterative deepening search which iteratively increases the term-depth bound. In the long version [6] of the current paper we prove soundness and completeness of our generic evaluation method and show that, when the term-depth bound is fixed, the method has PTIME data complexity. In [6] we also propose two exemplary control strategies: one is to reduce the number of accesses to the secondary storage, while the other is depth-first search. © 2012 Springer-Verlag.


Chi K.P.,Vinh University | Karapinar E.,Atilim University | Thanh T.D.,Vinh University
Mathematical and Computer Modelling | Year: 2012

In this paper, we prove fixed point theorems for generally contractive mappings in complete partial metric spaces. Theorems presented are generalizations of recent fixed point theorems of D. Ilić, V. Pavlović, and V. Rakocević. An example is also stated that illustrates our results are extensions of their theorems. © 2011 Elsevier Ltd.


Quang N.V.,Vinh University | Thuan N.T.,Vinh University
Fuzzy Sets and Systems | Year: 2012

In this paper, we establish some strong laws of large numbers for double adapted arrays of set-valued and fuzzy-valued random variables in separable Banach space. Our results are obtained with and without conditionally compactly uniformly integrable hypothesis, and they are more general than some related results. © 2012 Elsevier B.V.


Hao D.N.,Hanoi Institute of Mathematics | Van Duc N.,Vinh University
Inverse Problems | Year: 2011

Let H be a Hilbert space with the norm ∥ ∥ and A(t) (0 ≤ t ≤ T ) be positive self-adjoint unbounded operators from D(A(t)) ⊂ H to H. In the paper, we establish stability estimates of Hölder type and propose a regularizationmethod for the ill-posed-backward parabolic equation with time-dependent coefficients {ut + A(t)u = 0, 0 < t < T{ ∥u(T ) - f ∥ ≤ ε, f ε H, ε > 0. Our stability estimates improve the related results by Krein (1957 Dokl. Akad. Nauk SSSR 114 1162-5), and Agmon and Nirenberg (1963 Commun. Pure Appl. Math. 16 121-239). Our regularization method with a priori and a posteriori parameter choice yields error estimates of Hölder type. This is the only result when a regularization method for backward parabolic equations with time-dependent coefficients provides a convergence rate. © 2011 IOP Publishing Ltd.


Hoa N.T.Q.,Vinh University | Huyen D.N.,Hanoi University of Science and Technology
Journal of Materials Science: Materials in Electronics | Year: 2013

We report a comparative study of room temperature ferromagnetism (RTFM) in undoped and Ni-doped TiO2 nanowires synthesized by solvothermal method. Both undoped and Ni-doped TiO2 nanowire samples showed the RTFM with coercive field of ∼125 Oe due to intrinsic effect. Interestingly, compared to the doped TiO2 nanowires, the undoped nanowires exhibited the higher saturation magnetization value, indicating surface defects such as Ti3+ and oxygen vacancy play more important role in realizing RTFM than Ni doping. The origin of RTFM in the undoped nanowires can be attributed to the ferromagnetic coupling between Ti3+ ions via F+ center resulting from oxygen vacancy on the nanowire surface. Furthermore, saturation magnetization value of the doped nanowires is increased with increasing the doping concentration due to the enhanced ferromagnetic coupling between Ni2+ ions via F+ center. © 2012 Springer Science+Business Media, LLC.


Nguyen H.Q.,Vinh University
Advances in Natural Sciences: Nanoscience and Nanotechnology | Year: 2010

We have performed a conventional and non-coordinated-based method for synthesis of CdSe and CdSe/ZnS core/shell quantum dots in this work. This was the first time a CdSe/ZnS core/shell structure was successfully synthesized in a non-coordinating solvent without trioctylphosphine oxide (TOPO). The obtained CdSe nanocrystals were characterized by using UV-Vis absorption spectroscopy, photoluminescent (PL) spectroscopy and transmission electron microscopy (TEM), which confirmed that a series of CdSe particles with a diameter of 1.9-3.5 nm, corresponding to the first peak of absorption spectra in the 450-570 nm range, was successfully achieved. The CdSe/ZnS core/shell structures were then fabricated by coating the previously synthesized CdSe core with various ZnS layers. These CdSe/ZnS semiconductor quantum dots exhibited very high photoluminescence in comparison to that of the original CdSe cores. The narrow width of the CdSe/ZnS quantum dots indicated that the as-produced quantum dots have uniform size distribution, desirable dispersibility and excellent fluorescent properties. These are the requirements for several potential utilizations, such as cellular imaging, biomedical sensing, and solar cell and other photovoltaic applications. © 2010 Vietnam Academy of Science & Technology.


Tung D.T.,Vinh University
Outlook on Agriculture | Year: 2016

The aim of this study was to measure the technical efficiency and productivity performance of livestock production activities across different regions of Vietnam, based on panel data covering the period 2008–2012. Although efficiency improvements did occur in some regions over this period, low technical efficiency, poor productivity performance, and variations in performance composition dominate across most regions. Households that depend heavily on the livestock income particularly or the agricultural income generally are more vulnerable than others in terms of livestock production. © The Author(s) 2016.


Cao S.T.,Vinh University
ACM International Conference Proceeding Series | Year: 2013

The aim of this paper is to analyze the efficiency of the QSQN method, which was proposed by us and Nguyen in [10] for evaluating queries to Horn knowledge bases. In order to compare QSQN with the well-known methods QSQR and the one based on the Magic-Set transformation, we have implemented all of these methods. We compare them using representative examples that appear in many articles on deductive databases. Our experimental results show that the QSQN method usually outperforms the two other methods. Apart from the experimental results, we also explain the reasons behind the good performance of QSQN. Copyright © 2013 ACM.

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