Da Lat, Vietnam

University of Dalat

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Hai D.T.,University of Dalat | Son L.H.,Vietnam National University, Hanoi | Vinh T.L.,Vietnam National University, Hanoi
Applied Soft Computing Journal | Year: 2017

In this paper, we consider the sensor-energy optimization in 3D Wireless Sensor Networks (WSNs), which determines an optimal topology of sensors to prolong the network lifetime and reduce the energy expenditure. A new mathematical model for clustering in 3D WSN, considering energy consumption, constraints of communication and a 3D energy function, is presented. Using the Lagrange multiplier method, solutions of the model consisting of cluster centres and the membership matrix are computed and used in the new algorithm, called FCM-3 WSN. Experimental validation on real 3D datasets demonstrates that FCM-3 WSN outperforms the relevant methods, namely, Low-Energy Adaptive Clustering Hierarchy (LEACH), Centralized LEACH (LEACH-C), Single-hop Clustering and Energy-Efficient Protocol (SCEEP), Hybrid-Low Energy Adaptive Clustering Hierarchy (H-LEACH), K-Means and Fuzzy C-Means (FCM). © 2017 Elsevier B.V.

Yang S.-H.,National Taipei University of Technology | Vo P.B.,University of Dalat
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2017

Scalable video coding (SVC) is a coding paradigm that allows once-encoded video content to be used in diverse scenarios. SVC-coded videos can be transmitted and rendered at specified bitrates according to network bandwidth and end device requirements. In this paper, an adaptive bit allocation algorithm is proposed for the emerging scalable High Efficiency Video Coding (SHVC) standard. The bit budget at the group-of-pictures level is allocated according to buffer occupancy. Picture complexity, measured using the predicted mean absolute difference (MAD), buffer occupancy, and hierarchical level, is proposed for regulating the bitrate at the picture level. The MAD of the current picture is predicted using a novel mean prediction error (MPE) model, which is obtained from the advanced motion vector prediction, and the test zone search specified in SHVC and the associated reference software of SHVC. Moreover, MPE is used to determine the number of assigned bits at the coding-tree-unit level. The bit budget of each level is incorporated with the R-λ model for computing the required quantization parameter. Experimental results reveal that the proposed method achieves accurate bitrates with enhanced and consistent visual quality and more satisfactorily controls buffer occupancy compared with the state-of-the-art approaches reported in the literature. © 1991-2012 IEEE.

Shih C.-H.,National Chi Nan University | Chien N.D.,University of Dalat
Journal of Computational Electronics | Year: 2017

The onset behavior of output characteristics in tunnel field-effect transistors (TFETs) importantly determines the performance of digital TFET-based circuits. In this paper, we analytically and numerically examine the dependence of the onset behavior of output characteristics on the bandgap of semiconductors in line-tunneling TFETs. The qualitative and quantitative analyses show that the output onset behavior in line-tunneling TFETs strongly depends on the bandgap because the roles of two factors, including the incident electron number and tunneling probability, in determining the variation of tunneling current under increasing drain voltage change oppositely when varying the bandgap. Particularly, the superlinear onset in line-tunneling TFETs can be effectively suppressed to reduce the saturation drain voltage by using low-bandgap semiconductors. Together with the advantages in on-current and subthreshold swing as shown previously, the significant superiority in output characteristic makes the use of low-bandgap materials to be an efficient approach for simultaneously enhancing the device and circuit performances of advanced line-tunneling TFETs. © 2017 Springer Science+Business Media, LLC

DInh S.T.,Institute of Mathematics | Pham T.S.,University of Dalat
International Journal of Mathematics | Year: 2016

Let F(x):= (fij(x))i,j=1,...,p, be a real symmetric polynomial matrix of order p and let f(x) be the largest eigenvalue function of the matrix F(x). We denote by f(x) the Clarke subdifferential of f at x. In this paper, we first give the following nonsmooth version of ojasiewicz gradient inequality for the function f with an explicit exponent: For any there exist c > 0 and > 0 such that we have for all )|1- 1 (2n+p(n+1),d+3), where d:=maxi,j=1,...,pdeg fij and is a function introduced by D'Acunto and Kurdyka: (n,d):= d(3d-3)n-1 if d ≥ 2 and (n,d):= 1 if d = 1. Then we establish some local and global versions of lojasiewicz inequalities which bound the distance function to the set {x n: f(x) ≤ 0} by some exponents of the function [f(x)]+:=max{f(x), 0}. © 2016 World Scientific Publishing Company.

Dinh S.-T.,Institute of Mathematics | Pham T.-S.,University of Dalat
Journal of Complexity | Year: 2016

Let F(x):=(fij(x))i=1,...,p;j=1,...,q, be a (p×q)-real polynomial matrix and let f(x) be the smallest singular value function of F(x). In this paper, we first give the following nonsmooth version of Łojasiewicz gradient inequality for the function f with an explicit exponent: For any x¯∈Rn , there exist c>0 and ε(lunate)>0 such that we have for all (norm of matrix)x-x¯(norm of matrix)<ε(lunate),. inf((norm of matrix)w(norm of matrix):w∈∂f(x))≥c|f(x)-f(x¯)|1-τ, where ∂f(x) is the limiting subdifferential of f at x , d:=maxi=1,...,p;j=1,...,qdegfij , ℛ(n,d):=d(3d-3)n-1 if d≥2 and ℛ(n,d):=1 if d=1, and τ:=1ℛ(n+p,2d+2). Then we establish some versions of Łojasiewicz inequality for the distance function with explicit exponents, locally and globally, for the smallest singular value function f(x) of the matrix F(x). © 2016 Elsevier Inc.

Pham T.S.,University of Dalat
Kodai Mathematical Journal | Year: 2012

Let f: R n → R be a polynomial function of degree d with f(0)= 0. The classical Łojasiewiz inequality states that there exist c > 0 and x > 0 such that {pipe}f (x){pipe} ≥ cd(x, f -1(0)) α in a neighbourhod of the origin 0∈R n, where d(x, f -1(0)) denotes the distance from x to the set f -1(0): We prove that the smallest such exponent α is not greater than R(n, d) with R(n, d): max{d(3d-4) n-1, 2d(3d-3) n-2}.

Vui H.H.,Institute of Mathematics | So'n P.T.,University of Dalat
SIAM Journal on Optimization | Year: 2010

This paper studies the representation of a positive polynomial f on a closed semialgebraic set S := {κ ∈ R n | gi(κ) = 0, i = 1, . . . , l, hj(κ) ≥ 0, j = 1, . . . ,m} modulo the so-called critical ideal I(f, S) of f on S. Under a constraint qualification condition, it is demonstrated that, if either f > 0 on S or f ? 0 on S and the critical ideal I(f, S) is radical, then f belongs to the preordering generated by the polynomials h1, . . . , hm modulo the critical ideal I(f, S). These facts imply that we can find a natural sequence of semidefinite programs whose optimal values converge monotonically, increasing to the infimum value f ? := inf κ∈S f(κ) of f on S, provided that the infimum value is attained at some point. Besides, we shall construct a finite set in R containing the infimum value f ?. Moreover, some relations between the Fedoryuk [Soviet Math. Dokl., 17 (1976), pp. 486-490] and Malgrange [Complex Analysis, Microlocal Calculus and Relativistic Quantum Theory, Lecture Notes in Phys. 126, Springer, Berlin, 1980, pp. 170-177] conditions and coercivity for polynomials, which are bounded from below on S, are also established. In particular, a sufficient condition for f to attain its infimum on S is derived from these facts. We also show that every polynomial f, which is bounded from below on S, can be approximated in the l1-norm of coefficients by a sequence of polynomials f ∈ that are coercive. Finally, it is shown that almost every linear polynomial function, which is bounded from below on S, attains its infimum on S and has the same asymptotic growth at infinity. © 2010 Society for Industrial and Applied Mathematics.

Duong H.,University of Dalat | Truong T.,University of Dalat | Vo B.,Ton Duc Thang University
Engineering Applications of Artificial Intelligence | Year: 2014

Constraint-based frequent itemset mining is necessary when the needs and interests of users are the top priority. In this task, two opposite types of constraint are studied, namely anti-monotone and monotone constraints. Previous approaches have mainly mined frequent itemsets that satisfy one of these two types of constraint. Mining frequent itemsets that satisfy both types is of interest. The present study considers the problem of mining frequent itemsets with the following two conditions: they include a set C0 (monotone) and contain no items of set C′1 (anti-monotone), where the intersection of C0 and C′1 is empty and they are changed regularly. A unique representation of frequent itemsets restricted on C0 and C′1 using closed itemsets and their generators is proposed. Then, an algorithm called MFS-DoubleCons is developed to quickly and distinctly generate all frequent itemsets that satisfy the constraints from the lattice of closed itemsets and generators instead of mining them directly from the database. The theoretical results are proven to be reliable. Extensive experiments on a broad range of synthetic and real databases that compare MFS-DoubleCons to dEclat-DC (a modified version of dEclat utilized to mine frequent itemsets with constraints) show the effectiveness of our approach. © 2013 Elsevier Ltd.

Huong Giang N.T.,Asian Institute of Technology | Huong Giang N.T.,University of Dalat | Kim Oanh N.T.,Asian Institute of Technology
Atmospheric Environment | Year: 2014

A monitoring program was designed and implemented to characterize roadside levels of PM2.5 and BTEX in Ho Chi Minh City, Vietnam, and to generate input data for CALINE (California LINE Source Dispersion Model) inverse modeling. Monitoring was done during Dec 2007-Jan 2008, on both weekdays and weekends, and yielded 284 hourly BTEX samples (adsorption tubes), 24 samples of 8h-PM2.5 and 42 samples of 24h-PM2.5 (by MiniVol samplers). The air sampling was done at 8 points on both sides of one street that had an average traffic flow, simultaneously meteorology data and vehicle flows were recorded. Roadside 24h-PM2.5 levels were 97±31 (53-151) μgm-3, higher on weekdays than weekends. Diurnal BTEX variation patterns were consistent with the diurnal flows of 6 vehicle categories moving on the street. BTEX levels were reduced with the increase in downwind distance from traffic lanes (approximately by 15% for each 5m increment). Principal component analysis also confirmed the association between roadside pollution levels and traffic. A calculation algorithm was developed to remove the urban background, contributed by other sources than traffic in the selected street, from the roadside measured pollution levels. Urban background contributed a majority of PM2.5 (90-98%) and hourly BTEX (67-97%) with higher contributions at upwind side of the street and at late evening hours when less traffic was observed. CALINE inverse modeling produced explainable fleet hourly emission rates (gkm-1h-1) and vehicle emission factors (EF, mgveh-1km-1). The obtained EF for gasoline and diesel vehicles were comparable with recent measurements made in Asian cities, as well as with calculated EFs for European and US urban fleets about 10-15 years ago. To minimize the collinearity problem encountered in inverse traffic modeling it is essential that the monitoring is done at different times to capture significant variations in the street traffic compositions. © 2014 Elsevier Ltd.

Truong T.C.,University of Dalat | Tran A.N.,University of Dalat
Studies in Computational Intelligence | Year: 2010

It is important to propose effective algorithms that find basic association rules and generate all consequence association rules from those basic rules. In this paper, we propose the new concept of eliminable itemset to show how to represent itemset by generators and eliminable itemsets. Using algebraic approach based on equivalence relations, we propose a new approach to partition the set of association rules into basic and consequence sets. After describing their strict relations, we propose two ways to derive all consequence association rules from the basic association rules. These two ways satisfy the properties: sufficiency, preserved confidence. Moreover, they do not derive repeated consequence rules. Hence, we save much time for discovering association rule mining. © 2010 Springer-Verlag Berlin Heidelberg.

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