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.

Chien N.D.,University of Dalat | Shih C.-H.,National Chi Nan University
Superlattices and Microstructures | Year: 2016

The heterojunction technique has recently been considered as an effective approach to simultaneously achieve a high on-current and low ambipolar off-leakage in tunnel field-effect transistors (TFETs). In this paper, we propose the various configurations of abrupt and graded Si/SiGe heterojunctions for TFETs and investigate their short-channel effects by using two-dimensional simulations. It is shown that the semiconductor bandgap has to be properly considered together with the drain-induced barrier thinning in studying short-channel effects because scaling down the bandgap considerably deteriorates short-channel effects in TFETs. Among the basic configurations of Si/SiGe heterojunctions, the slantingly graded Si/SiGe heterostructure is most excellent in optimizing the electrical characteristics of the extremely scaled TFETs without short-channel effects. The slantingly graded Si/SiGe TFET with superior short-channel performance exhibits a potential device for low power and high packaging density integrated circuits. © 2016 Elsevier Ltd.

DAng V.D.,Thang Long High School For Gifted | Ha H.V.,Vietnam Academy of Science and Technology | Pham T.-S.,University of Dalat
SIAM Journal on Optimization | Year: 2016

In this paper, we consider the collection of unconstrained polynomial optimization problems, in which every problem of the collection is obtained by perturbations of coefficients of the cost function. The main result states that there exists an open and dense semialgebraic set UΓ in the corresponding Euclidean space of data such that for every polynomial f∈ UΓ, which is bounded from below on ℝn, the problem of minimization of f over ℝn is strongly well-posed. © 2016 Society for Industrial and Applied Mathematics.

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.

Tran A.,University of Dalat | Truong T.,University of Dalat | Le B.,Ho Chi Minh City University of Natural Sciences
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

This paper shows a mathematical foundation for almost important features in the problem of discovering knowledge by association rules. The class of frequent itemsets and the association rule set are partitioned into disjoint classes by two equivalence relations based on closures. Thanks to these partitions, efficient parallel algorithms for mining frequent itemsets and association rules can be obtained. Practically, one can mine frequent itemsets as well as association rules just in the classes that users take care of. Then, we obtain structures of each rule class using corresponding order relations. For a given relation, each rule class splits into two subsets of basic and consequence. The basic one contains minimal rules and the consequence one includes in the rules that can be deducted from those minimal rules. In the rest, we consider association rule mining based on order relation min. The explicit form of minimal rules according to that relation is shown. Due to unique representations of frequent itemsets through their generators and corresponding eliminable itemsets, operators for deducting all remaining rules are also suggested. Experimental results show that mining association rules based on relation min is better than the ones based on relations of minmin and minMax in terms of reduction in mining times as well as number of basic rules. © 2012 Springer-Verlag.

Tran A.,University of Dalat | Truong T.,University of Dalat | Le B.,Ho Chi Minh City University of Natural Sciences
Studies in Computational Intelligence | Year: 2013

Closed itemsets and their generators play an important role in frequent itemset and association rule mining since they lead to a lossless representation of all frequent itemsets. The previous approaches discover either frequent closed itemsets or generators separately. Due to their properties and relationship, the paper proposes GENCLOSE thatmines them concurrently. In a level-wise search, it enumerates the generators using a necessary and sufficient condition for producing (i+1)-item generators from i-item ones. The condition is designed based on object-sets which can be implemented efficiently using diffsets, is very convenience and is reliably proved. Along that process, pre-closed itemsets are gradually extended using three proposed expanded operators. Also, we prove that they bring us to expected closed itemsets. Experiments on many benchmark datasets confirm the efficiency of GENCLOSE. © 2013 Springer International Publishing Switzerland.

Tran A.,University of Dalat | Truong T.,University of Dalat | Le B.,Vietnam National University, Ho Chi Minh City
Advances in Intelligent Systems and Computing | Year: 2014

When the number of association rules extracted from datasets is very large, using them becomes too complicated to the users. Thus, it is important to obtain a small set of association rules in direction to users. The paper investigates the problem of discovering the set of association rules intersected with constraint itemsets. Since the constraints usually change, we start the mining from the lattice of closed itemsets and their generators, mined only one time, instead of from the dataset. We first partition the rule set with constraint into disjoint classes of the rules having the same closures. Then, each class is mined independently. Using the set operators on the closed itemsets and their generators, we show the explicit representations of the rules intersected with constraints in two shapes: rules with confidence of equal to 1 and those with confidence of less than 1. Due to those representations, the algorithm IntARS-OurApp is proposed for mining quickly the rules without checking rules directly with constraints. The experiments proved its efficiency. © Springer International Publishing Switzerland 2014.

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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