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Quang Vu Bach,한동근,최지연,정윤기,박방주 한국고분자학회 2012 Macromolecular Research Vol.20 No.9
A series of hybrid nanocomposites containing poly(L-lactide) (PLLA) and polyhedral oligomeric silsesquioxane (POSS) was prepared by solvent casting method for the enhancement of the mechanical properties of PLLA. One of them was mixed by only a physical blending between PLLA and POSS to form PLLA/POSS nanocomposite that did not show considerable improvement. In the other hand, two types of PLLA-POSS additives were synthesized via the ring-opening polymerization of L-lactide in the presence of POSS in different content. On these additives, POSS played as not only an initiator for the ring-opening polymerization reaction due to its hydroxyl functional groups on the surface but also a type of hybrid filler for PLLA/PLLA-POSS nanocomposite after mixing with PLLA matrix. PLLA/PLLA-POSS composite showed significant improvement in mechanical properties because of covalent bonding between PLLA and POSS. In particular, the tensile modulus has been apparently increased in PLLA/5PLLA-5POSS nanocomposites (1,449 MPa) with respect to PLLA control (498 MPa). SEM and XRD data indicated that the dispersion of PLLA-modified POSS was better than that of POSS in PLLA matrix. Although the contact angle was not significantly different, the protein adsorption and platelet adhesion are reduced slightly in PLLA/PLLA-POSS nanocomposite as compared to those of PLLA control and PLLA/POSS. Therefore,it is expected that biodegradable POSS nanocomposite may be helpful to be utilized in biomedical devices such as drug-eluting stents and artificial implants
Energy-Efficient Bandwidth and Power Allocation for Multi-Homing Networks
Quang-Doanh Vu,Le-Nam Tran,Juntti, Markku,Een-Kee Hong Institute of Electrical and Electronics Engineers 2015 IEEE transactions on signal processing Vol. No.
<P>This paper investigates resource allocation for multi-homing networks where users can simultaneously transmit data to multiple radio access networks (RANs) using multiple air interfaces. We aim at optimally assigning the bandwidth and power to each user-RAN connection so as to maximize energy-efficiency of the entire network subject to user specific QoS requirements as well as the available resource budgets. First, we study the problem of resource allocation for scenarios where the connections between the users and the RANs are predefined, which naturally leads to a fractional program. To obtain the optimal solution efficiently and facilitate distributed implementations, we further equivalently transform the design problem into a convex program using a parameter-free approach and develop a decentralized algorithm based on the alternating direction method of multipliers. Second, we investigate the problem of joint link selection and resource allocation for energy-efficiency maximization. The problem is cast as a mixed integer nonlinear convex program for which we particularize the branch and bound method to find an optimal solution. Then, two suboptimal low-complexity designs are proposed: the first one is based on greedy algorithm, which gradually maximizes the virtual link energy-efficiency; the other one is based on the concept of sparsity-inducing norm. Simulation results are presented to demonstrate the potential gains in terms of energy-efficiency of the proposed methods.</P>
Energy-Efficient Zero-Forcing Precoding Design for Small-Cell Networks
Quang-Doanh Vu,Le-Nam Tran,Farrell, Ronan,Een-Kee Hong Institute of Electrical and Electronics Engineers 2016 IEEE Transactions on Communications Vol. No.
<P>We consider small-cell networks with multiple-antenna transceivers and base stations (BSs) cooperating to jointly design linear precoders to maximize the network energy efficiency, subject to a sum power and per-antenna power constraints at individual BSs, as well as user-specific quality of service (QoS) requirements. Assuming zero-forcing precoding, we formulate the problem of interest as a concave-convex fractional program to which we proposed a centralized optimal solution based on the prevailing Dinkelbach algorithm. To facilitate distributed implementations, we transform the design problem into an equivalent convex program using Charnes-Cooper's transformation. Then, based on the framework of alternative direction method of multipliers (ADMM), we develop a decentralized algorithm, which is numerically shown to achieve fast convergence. Since BSs are generally power-hungry, it may be more energy-efficient if some BSs can be shut down, while still satisfying the QoS constraints. Toward this end, we investigate the problem of joint precoder design and BS selection, which is a mixed Boolean nonlinear program, and then provide an optimal solution by customizing the branch-and-bound method. For real-time applications, we propose a greedy algorithm which achieves near-optimal performance in polynomial time. Numerical results are provided to demonstrate the effectiveness of the proposed algorithms.</P>
Vu, Quang Dao,Nguyen, Thanh Binh,Chung, Sun-Tae Korea Multimedia Society 2017 멀티미디어학회논문지 Vol.20 No.6
In this paper, we propose a simple online multiple object (human) tracking method, LKDeep (Lucas-Kanade feature and Detection based Simple Online Multiple Object Tracker), which can run in fast online enough on CPU core only with acceptable tracking performance for embedded surveillance purpose. The proposed LKDeep is a pragmatic hybrid approach which tracks multiple objects (humans) mainly based on LK features but is compensated by detection on periodic times or on necessity times. Compared to other state-of-the-art multiple object tracking methods based on 'Tracking-By-Detection (TBD)' approach, the proposed LKDeep is faster since it does not have to detect object on every frame and it utilizes simple association rule, but it shows a good object tracking performance. Through experiments in comparison with other multiple object tracking (MOT) methods using the public DPM detector among online state-of-the-art MOT methods reported in MOT challenge [1], it is shown that the proposed simple online MOT method, LKDeep runs faster but with good tracking performance for surveillance purpose. It is further observed through single object tracking (SOT) visual tracker benchmark experiment [2] that LKDeep with an optimized deep learning detector can run in online fast with comparable tracking performance to other state-of-the-art SOT methods.
Vu, Pham-Quang,Choi, Kwang-Il,Oh, Jong-Taek,Cho, Honggi World Scientific Publishing Co. Pte. Ltd. 2017 International Journal of Air-Conditioning and Refr Vol.25 No.2
<P>The condensation heat transfer coefficients and pressure drops of R410A and R22 flowing inside a horizontal aluminum multiport mini-channel tube having 18 channels are investigated. Experimental data are presented for the range of vapor quality from 0.1 to 0.9, mass flux from 50 to 500<TEX>$ \,$</TEX>kg/m<SUP>2</SUP>s, heat flux from 3 to 15<TEX>$ \,$</TEX>kW/m<SUP>2</SUP> and the saturation temperature at 48<TEX>$ ^{\circ }$</TEX>C. The pressure drop across the test section was directly measured by a differential pressure transducer. At a small scale, the noncircular cross-sections can enhance the effect of the surface tension. The average heat transfer coefficient increased with the increase of vapor quality, mass flux and heat flux. Under the same test conditions, the heat transfer coefficients of R22 are higher than those for R410A, the pressure drops for R410A are 7-19% lower than those of R22. The lower pressure drop of R410A has an important advantage as an alternative working fluid for R22 in air-conditioning and heat pump systems.</P>
Vu Dinh Quang,Nguyen Dinh Khoa,Nguyen Dinh Duc 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.8
This research examines the influent of structural characteristics (shape, size, material properties, porosity), external conditions (mechanical load, thermal load, and foundation parameters) on the vibration and nonlinear dynamic response of shear deformable porous plates made of functionally graded materials (FGM) in the thermal environment and rested on the Pasternak’s elastic foundation. Reddy’s third-order shear deformation theory (TSDT) and von Kármán’s geometric nonlinearity are used to explore the structural behavior of thick FGM porous plates with two types of porosity distribution in FGM porous plates namely, even and uneven patterns. The solutions are obtained through the Bubnov-Galerkin method and RungeKutta methods. The outcomes are compared with other research in the result section to assess the reliability of the solution method in the paper.