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Modeling of Unsteady Laminar Flow Based on Steady Solution in Jetting Dispensing Process
Quoc Hung Nguyen,Seung-Bok Choi IEEE 2008 IEEE transactions on electronics packaging manufac Vol.31 No.2
<P>This paper proposes a new approach to model unsteady laminar flows of dispenser systems in the semiconductor packaging industry. The approach is based on the exact steady solution. After an overview of dispensing technology and historical modeling of the unsteady flows, a new modeling approach of the unsteady laminar flow in a circular pipe and annular duct is developed. From the proposed model, the modeling results of unsteady flow in an arbitrary circular pipe and annular duct are obtained and compared with the spectral solution. In addition, a comparative work between the proposed analytical dynamic model and the finite-element model is undertaken in order to demonstrate the effectiveness of the proposed modeling methodology.</P>
Simulation of non-dilute fibre suspensions using RBF-based macro–micro multiscale method
Hung Quoc Nguyen,Canh-Dung Tran 한국유변학회 2022 Korea-Australia rheology journal Vol.34 No.1
The multiscale stochastic simulation method based on the marriage of the Brownian Configuration Field (BCF) and the Radial Basis Function mesh-free approximation for dilute fibre suspensions by our group, is further developed to simulate non-dilute fibre suspensions. For the present approach, the macro and micro processes proceeded at each time step are linked to each other by a fibre contributed stress formula associated with the used kinetic model. Due to the feature of non-dilute fibre suspensions, the interaction between fibres is introduced into the evolution equation to determine fibre configurations using the BCF method. The fibre stresses are then determined based on the fibre configuration fields using the Phan–Thien–Graham model. The efficiency of the simulation method is demonstrated by the analysis of the two challenging problems, the axisymmetric contraction and expansion flows, for a range of the fibre concentration from semi-dilute to concentrated regimes. Results evidenced by numerical experiments show that the present method would be potential in analysing and simulating various suspensions in food and medical industries.
Quoc-Hung Pham,Jyh-Chen Chen,Huy-Bich Nguyen 한국광학회 2020 Current Optics and Photonics Vol.4 No.4
In this study, the traditional electron-blocking layer (EBL) in (In,Ga)N/GaN light-emitting diodes is replaced by a circular EBL that is the same size as the n-pad. The three-dimensional (3D) nonlinear Poisson, drift-diffusion, and continuity equations are adopted to simulate current transport in the LED and its characteristics. The results indicate that the local carrier-density distribution obtained for the circular EBL design is more uniform than that for the traditional EBL design. This improves the uniformity of local radiative recombination and local internal quantum efficiency (IQE) at high injection levels, which leads to a higher lumped IQE and lower efficiency droop. With the circular EBL, the lumped IQE is higher in the outer active region and lower in the active region under the n-pad. Since most emissions from the active region under the n-pad are absorbed by the n-pad, obviously, an LED with a circular EBL will have a higher external quantum efficiency (EQE). The results also show that this LED works at lower applied voltages.
EXISTENCE OF WEAK NON-NEGATIVE SOLUTIONS FOR A CLASS OF NONUNIFORMLY BOUNDARY VALUE PROBLEM
Hang, Trinh Thi Minh,Toan, Hoang Quoc Korean Mathematical Society 2012 대한수학회보 Vol.49 No.4
The goal of this paper is to study the existence of non-trivial non-negative weak solution for the nonlinear elliptic equation: $$-div(h(x){\nabla}u)=f(x,u)\;in\;{\Omega}$$ with Dirichlet boundary condition in a bounded domain ${\Omega}{\subset}\mathbb{R}^N$, $N{\geq}3$, where $h(x){\in}L^1_{loc}({\Omega})$, $f(x,s)$ has asymptotically linear behavior. The solutions will be obtained in a subspace of the space $H^1_0({\Omega})$ and the proofs rely essentially on a variation of the mountain pass theorem in [12].
Bioactive Constituents from the n-Butanolic Fraction of Aruncus dioicus var. kamtschaticus
Quoc Hung Vo,Phi Hung Nguyen,Bing Tian Zhao,Yen Nguyen Thi,Duc Hung Nguyen,김원일,서유민,민병선,우미희 한국생약학회 2014 Natural Product Sciences Vol.20 No.4
Six compounds were isolated from the n-BuOH fraction of the aerial parts of Aruncus dioicus var. kamtschaticus including: sambunigrin (1), prunasin (2), aruncide A (3), aruncide C (4), 1-O-caffeoyl-β-D-glucopyranose (5), and caffeic acid (6). Their structures were confirmed by comparing the spectral data with those reported in the literature. The isolated compounds (1 - 6) were then examined for their cytotoxic effects towards MCF-7, HL-60, and HeLa cancer cell lines, as well as their DPPH radical scavenging activity. The results indicated that compound 4 possessed the strongest inhibitory effect toward HeLa cell line with IC50 value of 5.38 ± 0.92 μM. Compound 3 possessed selective cytotoxic activity on HL-60 cells with IC50 value of 6.27 ± 0.17 μM, compound 5 was found as the best in inhibiting proliferation with IC50 value of 2.25 ± 0.09 μM, and the other compounds showed significant inhibition with IC50 values ranging from 6.10 to 11.27 μM. Compound 5 also displayed the strongest cytotoxic effect toward MCF-7 cell line (IC50 4.32 ± 0.15 μM). Both 5 and 6 demonstrated strong radical scavenging activity (IC50 6.87 ± 0.03 and 4.33 ± 0.22 μM, respectively). Compounds 1 and 5 were isolated for the first time from this plant.
Hang, Trinh Thi Minh,Toan, Hoang Quoc Korean Mathematical Society 2011 대한수학회보 Vol.48 No.6
In this paper we study the existence of non-trivial weak solutions of the Neumann problem for quasilinear elliptic equations in the form $$-div(h(x){\mid}{\nabla}u{\mid}^{p-2}{\nabla}u)+b(x){\mid}u{\mid}^{p-2}u=f(x,\;u),\;p{\geq}2$$ in an unbounded domain ${\Omega}{\subset}\mathbb{R}^N$, $N{\geq}3$, with sufficiently smooth bounded boundary ${\partial}{\Omega}$, where $h(x){\in}L_{loc}^1(\overline{\Omega})$, $\overline{\Omega}={\Omega}{\cup}{\partial}{\Omega}$, $h(x){\geq}1$ for all $x{\in}{\Omega}$. The proof of main results rely essentially on the arguments of variational method.
A Novel Scheme for Seamless Hand-off in WMNs
( Hung Quoc Vo ),( Daesun Kim ),( Choong Seon Hong ),( Sungwon Lee ),( Eui-nam Huh ) 한국인터넷정보학회 2009 KSII Transactions on Internet and Information Syst Vol.3 No.4
Although current wireless mesh network (WMN) applications experience a perceptually uninterrupted hand-off, their throughput after the hand-off event may be significantly degraded due to the low available bandwidth of the mobile client`s new master. In this paper, we propose a novel mobility management scheme for 802.11-based WMNs that enables both seamless hand-off for transparent communications, and bandwidth awareness for stable application performance after the hand-off process. To facilitate this, we (i) present a new buffer moment in support of the fast Layer-2 hand-off mechanism to cut the packet loss incurred in the hand-off process to zero and (ii) design a dynamic admission control to grant joining accepts to mesh clients. We evaluate the benefits and drawbacks of the proposal for both UDP and TCP traffic, as well as the fairness of the proposal. Our results show that the new scheme can not only minimize hand-off latency, but also maintain the current application rates of roaming users by choosing an appropriate new master for joining.