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


Tung D.T.,Vinh University
Outlook on Agriculture | Year: 2017

This study aims to assess levels of on-farm diversification in Vietnam. The results reflect regional differences in terms of on-farm diversification and its determinants. Households in northern regions have adapted to the fragmented and smallsized parcels of land by diversifying their on-farm activities. In contrast, the Mekong Delta region in the south of Vietnam is characterized by larger agricultural parcels and a specialization in rice production. Land use fragmentation, as reflected by a large number of plots in a given area, is one of the most important reasons for the high levels of on-farm diversification, while the higher share of non-farm income in total income is the reason of lower levels of on-farm diversification. Households have reacted to natural and economic shocks by diversifying their on-farm activities. The non-stationary Markov chain model used here shows various diversification scenarios and trends. In most cases, the on-farm diversification is expected to reduce in coming years. © The Author(s) 2017.


Chieu N.H.,Vinh University | Van Hien L.,Ha Tinh University
SIAM Journal on Optimization | Year: 2017

Let γ := fx 2 Rn j q(x) ϵ Θ}; where q : Rn → Rm is a twice continuously differentiable mapping, and Θ is a nonempty polyhedral convex set in Rm: In this paper, we first establish a formula for exactly computing the graphical derivative of the normal cone mapping N→ : Rn → Rn; x→ Nγ (x); under the condition that Mq(x) := q(x) - Θ is metrically subregular at the reference point. Then, based on this formula, we exhibit formulas for computing the graphical derivative of solution mappings and present characterizations of the isolated calmness for a broad class of generalized equations. Finally, applying this to optimization, we get a new result on the isolated calmness of stationary point mappings.


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.


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.


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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