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Search Results: 1 - 10 of 722 matches for " Dzung Phan "
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An ellipsoidal branch and bound algorithm for global optimization
William Hager,Dzung Phan
Mathematics , 2009,
Abstract: A branch and bound algorithm is developed for global optimization. Branching in the algorithm is accomplished by subdividing the feasible set using ellipses. Lower bounds are obtained by replacing the concave part of the objective function by an affine underestimate. A ball approximation algorithm, obtained by generalizing of a scheme of Lin and Han, is used to solve the convex relaxation of the original problem. The ball approximation algorithm is compared to SEDUMI as well as to gradient projection algorithms using randomly generated test problems with a quadratic objective and ellipsoidal constraints.
A Comparison of Control Methods for Z-Source Inverter  [PDF]
Cong-Thanh Pham, Anwen Shen, Phan Quoc Dzung, Nguyen Bao Anh, Nguyen Xuan Phu
Energy and Power Engineering (EPE) , 2012, DOI: 10.4236/epe.2012.44026
Abstract: In recent years, Z-source inverters (ZSI) have been proposed as an replacement power conversion concept which it has both voltage buck and boost abilities. In addition, ZSI doesn’t require dead-time to protection short circuit at two switches any of the same phase leg in the inverter bridge and to achieve optimal harmonic of current, voltage. This paper presents two different control methods (CM) for ZSI. The aim of this study to compare between two modulation methods, there are modi?ed space vector pulse width modulation method (MSVM) and the simple boost control (SBC) about the unique harmonic performance features, the total average and peak switching device power of the inverter system. In addition, this paper also analyzes about the ability exceed modulation index in linear region of two CM using MATLAB/Simulink.
Gradient-based methods for sparse recovery
William Hager,Dzung Phan,Hongchao Zhang
Mathematics , 2009,
Abstract: The convergence rate is analyzed for the SpaSRA algorithm (Sparse Reconstruction by Separable Approximation) for minimizing a sum $f (\m{x}) + \psi (\m{x})$ where $f$ is smooth and $\psi$ is convex, but possibly nonsmooth. It is shown that if $f$ is convex, then the error in the objective function at iteration $k$, for $k$ sufficiently large, is bounded by $a/(b+k)$ for suitable choices of $a$ and $b$. Moreover, if the objective function is strongly convex, then the convergence is $R$-linear. An improved version of the algorithm based on a cycle version of the BB iteration and an adaptive line search is given. The performance of the algorithm is investigated using applications in the areas of signal processing and image reconstruction.
An exact algorithm for graph partitioning
William Hager,Dzung Phan,Hongchao Zhang
Mathematics , 2009,
Abstract: An exact algorithm is presented for solving edge weighted graph partitioning problems. The algorithm is based on a branch and bound method applied to a continuous quadratic programming formulation of the problem. Lower bounds are obtained by decomposing the objective function into convex and concave parts and replacing the concave part by an affine underestimate. It is shown that the best affine underestimate can be expressed in terms of the center and the radius of the smallest sphere containing the feasible set. The concave term is obtained either by a constant diagonal shift associated with the smallest eigenvalue of the objective function Hessian, or by a diagonal shift obtained by solving a semidefinite programming problem. Numerical results show that the proposed algorithm is competitive with state-of-the-art graph partitioning codes.
The Shifts of Band Gap and Binding Energies of Titania/Hydroxyapatite Material
Nguyen Thi Truc Linh,Phan Dinh Tuan,Nguyen Van Dzung
Journal of Composites , 2014, DOI: 10.1155/2014/283034
Abstract: The titania/hydroxyapatite (TiO2/HAp) product was prepared by precipitating hydroxyapatite in the presence of TiO(OH)2 gel in the hydrothermal system. The characteristics of the material were determined by using the measurements such as X-ray photoemission spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance spectra (DRS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX). The XPS analysis showed that the binding energy values of Ca (2p1/2, 2p3/2), P (2p1/2, 2p3/2), and O 1s levels related to hydroxyapatite phase whereas those of Ti (2p3/2, 2p1/2) levels corresponded with the characterization of titanium (IV) in TiO2. The XRD result revealed that TiO2/HAp sample had hydroxyapatite phase, but anatase or rutile phases were not found out. TEM image of TiO2/HAp product showed that the surface of the plate-shaped HAp particles had a lot of smaller particles which were considered as the compound of Ti. The experimental band gap of TiO2/HAp material calculated by the DRS measurement was 3.6?eV, while that of HAp pure was 5.3?eV and that of TiO2 pure was around 3.2?eV. The shift of the band gap energy of TiO2 in the range of 3.2–3.6?eV may be related to the shifts of Ti signals of XPS spectrum. 1. Introduction TiO2 photocatalysis has gained much attention because of its low cost, nontoxicity, high stability, and easy preparation. However, the slow rates of the photocatalytic chemical transformations, compared with other methods, the low quantum yields, the lack of visible-light utilization, and the low adsorption capacity of TiO2 have hindered it from the practical application. To solve these problems, much effort has been made to enhance the photocatalytic efficiency and visible-light utilization of TiO2 by the additional components doping [1], improving its sensitization and metallization [2], or combining TiO2 and absorbable inorganic materials [3]. Recently, the preparation of titania/hydroxyapatite (TiO2/HAp) materials was attracting considerable attention thanks to the photocatalytic property of TiO2 and great adsorption ability of HAp. Among various features of the TiO2/HAp material which have been studied, the band gap evaluation was an important one because it decided the energy separation between the valence and conduction bands, the quantum effect, and the effect of visible-light utilization of that material [4]. The band gap of HAp was reported in [5] to be 3.95?eV by photoluminescence measurement, meanwhile, in some papers, that of HAp was calculated to be around 4.51–5.4?eV
Self-Tuning Fuzzy PI-Type Controller in Z-Source Inverter for Hybrid Electric Vehicles
PHAM CONG THANH,AnWen Shen,Phan Quoc Dzung,Nguyen Bao Anh
International Journal of Power Electronics and Drive Systems , 2012, DOI: 10.11591/ijpeds.v2i4.571
Abstract: This paper presents new algorithms to control speed induction motor (SIM) and the peak dc-link voltage (PDV) across the inverter bridge in z-source inverters (ZSI) by applying self-tuning fuzzy PI controller (SFP) with robust structure and non-linear characteristic. In particular, this so-called SFP based control algorithm (SFPA) is applied to a closed loop speed control system of induction motor, which relies on direct torque control scheme combined with modified space vector modulation (DTCMSVM) control strategy with so many exceptional features (e.g. fast torque response, low steady state torque ripple, and high accurate). Additionally, SFPA is used to control SIM and PDV are more adaptive to the sudden change of parameters such as load torque, stator resistance and dc input voltage (DIV), respectively. The transient response of SIM and PDV are thus improved with less over shoot, short rise time, small steady-state error and fast settling time, with low disturbance for output voltage stabilization in the inverter bridge. As a result, we achieve higher accuracy and robustness of SIM control system. Our new SFPA is verified in both simulation and experimental implementation using MATLAB and dSPACE DS1103, respectively.
Study on Current Public Opinion in Vietnam Based on Universally Value System and Core Values Approach  [PDF]
Phan Tan
Open Journal of Social Sciences (JSS) , 2015, DOI: 10.4236/jss.2015.32015
Abstract: The history of Vietnam Country’s formation and defense through thousands of years has been summarized in the modern society’s objective value systems that are: independence, freedom, happiness, prosperous people and strong country, democracy, justice, and civilization. The value of democracy is regarded a core value and it has been realistic by applying the mechanism of the fact that the people know, people discuss, people do, and people supervise. The author looks forward to clarify this mechanism, and, above all, in a certain degree of clarification it matches with manner forming public opinion, the roles and functions of the public opinion.
Micro Transportation Systems: A Review  [PDF]
Phuc Hong Pham, Dzung Viet Dao
Modern Mechanical Engineering (MME) , 2011, DOI: 10.4236/mme.2011.12005
Abstract: This paper summarized and reviewed recent studies of micro transportation systems (MTS) in the MEMS (Micro Electro-Mechanical System) field. Micro transportation systems can be identified and classified into three categories based on the contact types between the objects and the actuators (i.e. liquid-based, solid- based and air-bearing type). Their advantages and disadvantages were also analyzed and compared. The au- thors have proposed and developed three types of solid-based MTS utilizing electrostatic comb-drive actua- tors and ratchet mechanisms to drive the micro container in straight and curved paths. These MTSs have been fabricated with silicon-on-insulator (SOI)-MEMS technology and tested successfully. In the near future, MTSs can be applied in different fields such as medicine (to classify and test blood cells), in bioengineering (to capture, sort and combine bio-cells, DNA), or in micro robot systems.
The dependence of the strength properties of soil on its physical state
Nguyen Phuong Dzung
Magazine of Civil Engineering , 2012,
Abstract: Soils of hydraulic facilities and foundations are basically in the unsaturated state. Strength properties of these soils inside of each building area may be extremely various and should be carefully studied. It especially applies to tropical and arid areas. Soils that are above ground waters can remain in the unsaturated state in the areas with temperate climate. Research results of the dependence of the soil strength on its physical state (density and moisture) are presented. It was found that increase in the soil density brings to increase in the angle of internal friction and cohesion, but increase in the moisture, on the contrary – to its decrease. Collapse mode of specimens tested in stabilometer depends on how the value of the effective vertical stress relates to preconsolidation pressure, determined by compression test.
Control of Multiagent Formations
Dzung Tran,Tansel Yucelen
Mathematics , 2015,
Abstract: This paper makes the first attempt to show how information exchange rules represented by a network having multiple layers (multiplex information networks) can be designed for enabling spatially evolving multiagent formations. Toward this goal, we consider the invariant formation problem and introduce a distributed control architecture that allows capable agents to spatially alter the resulting formation's density and orientation without requiring global information exchange ability.
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