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Department of Applied Mathematics
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1.Energy Dissipation During Impact of an Agglomerate Composed of Autoadhesive Elastic-Plastic Particles

Author:Liu, LF;Thornton, C;Shaw, SJ


Abstract:Discrete Element Method is used to simulate the impact of agglomerates consisting of autoadhesive, elastic-plastic primary particles. In order to explain the phenomenon that the elastic agglomerate fractures but the elastic-plastic agglomerate disintegrates adjacent to the impact site for the same impact velocity, we increase the impact velocity and lower the yield strength of the constituent particles of the agglomerate. We find that increasing the impact velocity can lead to the increased number of yielded contacts, and cause the elastic-plastic agglomerate to disintegrate faster. Mostly importantly, the energy dissipation process for the elastic-plastic agglomerate impact has been investigated together with the evolutions of the yielding contacts, and evolutions of velocity during impact.

2.Dual algorithm for truncated fractional variation based image denoising

Author:Liang, HX;Zhang, JL


Abstract:Fractional-order derivative is attracting more and more attention of researchers in image processing because of its better property in restoring more texture than the total variation. To improve the performance of fractional-order variation model in image restoration, a truncated fractional-order variation model was proposed in Chan and Liang [Truncated fractional-order variation model for image restoration, J. Oper. Res. Soc. China]. In this paper, we propose a dual approach to solve this truncated fractional-order variation model on noise removal. The proposed algorithm is based on the dual approach proposed by Chambolle [An algorithm for total variation minimisation and applications, J. Math Imaging Vis. 20 (2004), pp. 89-97]. Conversely, the Chambolle's dual approach can be treated as a special case of the proposed algorithm with fractional order . The work of this paper modifies the result in Zhang et al. [Adaptive fractional-order multi-scale method for image denoising, J. Math. Imaging Vis. 43(1) (2012), pp. 39-49. Springer Netherlands 0924-9907, Computer Science, pp. 1-11, 2011], where the convergence is not analysed. Based on the truncation, the convergence of the proposed dual method can be analysed and the convergence criteria can be provided. In addition, the accuracy of the reconstruction is improved after the truncation is taken.

3.Knowledge Discovery and Recommendation With Linear Mixed Model

Author:Chen, ZY;Zhu, SX;Niu, Q;Zuo, TY

Source:IEEE ACCESS,2020,Vol.8

Abstract:We give a concise tutorial on knowledge discovery with linear mixed model in movie recommendation. The versatility of mixed effects model is well explained. Commonly used methods for parameter estimation, confidence interval estimate and evaluation criteria for model selection are briefly reviewed. Mixed effects models produce sound inference based on a series of rigorous analysis. In particular, we analyze millions of movie rating data with LME4 R package and find solid evidences for a general social behavior: the young tend to be more censorious than senior people when evaluating the same object. Such a social behavior phenomenon can be used in recommender systems and business data analysis.

4.Full-shipload tramp ship routing and scheduling with variable speeds

Author:Wen, M;Ropke, S;Petersen, HL;Larsen, R;Madsen, OBG


Abstract:This paper investigates the simultaneous optimization problem of routing and sailing speed in the context of full-shipload tramp shipping. In this problem, a set of cargoes can be transported from their load to discharge ports by a fleet of heterogeneous ships of different speed ranges and load-dependent fuel consumption. The objective is to determine which orders to serve and to find the optimal route for each ship and the optimal sailing speed on each leg of the route so that the total profit is maximized. The problem originated from a real-life challenge faced by a Danish tramp shipping company in the tanker business. To solve the problem, a three-index mixed integer linear programming formulation as well as a set packing formulation is presented. A novel Branch-and-Price algorithm with efficient data preprocessing and heuristic column generation is proposed. The computational results on the test instances generated from real-life data show that the heuristic provides optimal solutions for small test instances and near-optimal solutions for larger test instances in a short running time. The effects of speed optimization and the sensitivity of the solutions to the fuel price change are analyzed. It is shown that speed optimization can improve the total profit by 16%% on average and the fuel price has a significant effect on the average sailing speed and total profit. (C) 2015 Elsevier Ltd. All rights reserved.

5.Profile Inference from Heterogeneous Data Fundamentals and New Trends

Author:Lu, X;Zhu, SX;Niu, Q;Chen, ZY


Abstract:One of the essential steps in most business is to understand customers' preferences. In a data-centric era, profile inference is more and more relaying on mining increasingly accumulated and usually anonymous (protected) data. Personalized profile (preferences) of an anonymous user can even be recovered by some data technologies. The aim of the paper is to review some commonly used information retrieval techniques in recommendation systems and introduce new trends in heterogeneous information network based and knowledge graph based approaches. Then business developers can get some insights on what kind of data to collect as well as how to store and manage them so that better decisions can be made after analyzing the data and extracting the needed information.

6.Equivalent Extensions to Caristi-Kirk's Fixed Point Theorem, Ekeland's Variational Principle, and Takahashi's Minimization Theorem

Author:Wu, ZL


Abstract:With a recent result of Suzuki (2001) we extend Caristi-Kirk's fixed point theorem, Ekeland's variational principle, and Takahashi's minimization theorem in a complete metric space by replacing the distance with a tau-distance. In addition, these extensions are shown to be equivalent. When the tau-distance is l.s.c. in its second variable, they are applicable to establish more equivalent results about the generalized weak sharp minima and error bounds, which are in turn useful for extending some existing results such as the petal theorem.

7.A Relaxed Dimensional Factorization preconditioner for the incompressible Navier-Stokes equations

Author:Benzi, M;Ng, M;Niu, Q;Wang, Z


Abstract:In this paper we introduce a Relaxed Dimensional Factorization (RDF) preconditioner for saddle point problems. Properties of the preconditioned matrix are analyzed and compared with those of the closely related Dimensional Splitting (DS) preconditioner recently introduced by Benzi and Guo [7]. Numerical results for a variety of finite element discretizations of both steady and unsteady incompressible flow problems indicate very good behavior of the RDF preconditioner with respect to both mesh size and viscosity. (C) 2011 Elsevier Inc. All rights reserved.

8.Symmetric Sweeping Algorithms for Overlaps of Quadrilateral Meshes of the Same Connectivity

Author:Xu, XH;Zhu, SX

Source:COMPUTATIONAL SCIENCE - ICCS 2018, PT III,2018,Vol.10862

Abstract:We propose a method to calculate intersections of two admissible quadrilateral meshes of the same connectivity. The global quadrilateral polygons intersection problem is reduced to a local problem that how an edge intersects with a local frame which consists 7 connected edges. A classification on the types of intersection is presented. By symmetry, an alternative direction sweep algorithm halves the searching space. It reduces more than 256 possible cases of polygon intersection to 34 (17 when considering symmetry) programmable cases of edge intersections. Besides, we show that the complexity depends on how the old and new mesh intersect.

9.Spectral analysis of the generalized shift-splitting preconditioned saddle point problem

Author:Ren, ZR;Cao, Y;Niu, Q


Abstract:A shift-splitting preconditioner was recently proposed for saddle point problems, which is based on a generalized shift-splitting of the saddle point matrix. We provide a new analysis to prove that the corresponding shift-splitting iteration method is unconditional convergent. To further show the efficiency of the shift-splitting preconditioner, the eigenvalue distribution of the shift-splitting preconditioned saddle point matrix is investigated. We show that all eigenvalues having nonzero imaginary parts are located in an intersection of two circles and all real eigenvalues are located in a positive interval. Numerical examples are given to confirm our theoretical results. (C) 2016 Elsevier B.V. All rights reserved.

10.Extension of Talenti's Inequality and Maximum Values Relative to Rearrangement Classes

Author:Emamizadeh, B;Liu, YC;Porru, G


Abstract:The article starts by revisiting and extending the Talenti's inequality where the sharpness of the extended inequality is also addressed. The process leading to the extension comprises two steps. First, an observation that the Talenti's inequality indeed can be formulated in terms of a rearrangement class. Second, proving that the inequality holds even when the rearrangement class is replaced by a much bigger (modulo trivial cases) set namely an appropriate closure of the class. The article then continues to introduce and explore a related maximization problem, associated to the classical Poisson equation, where the admissible set is the class of rearrangements of a given function. The article briefly explains the physical interest in this optimization problem. The existence of optimal solutions is proved and the optimality conditions they satisfy are explicitly derived. The particular case where the rearrangement class is built out of a characteristic function is also discussed.

11.Toward self-powered photodetection enabled by triboelectric nanogenerators

Author:Wen, Z;Fu, JJ;Han, L;Liu, YN;Peng, MF;Zheng, L;Zhu, YY;Sun, XH;Zi, YL


Abstract:Photodetectors have been demonstrated to have broad applications in optical communication, environmental protection, biomedical monitoring, and so on. However, the applications of these photodetectors face great challenges due to the difficulties in powering these vastly distributed detectors and their limited photoresponsivity. At the same time, the invention of triboelectric nanogenerators (TENGs) provides a novel way for generating a high-voltage low-current power supply with well-controllable output, making a promising approach to trigger photodetection. This review article summarizes the existing research work on combining TENGs with photodetectors through four different configurations. These research studies achieved self-powered or active photodetectors enabled by TENGs, explored the novel photodetection mechanisms, and demonstrated TENG output for enhancing the photoresponsivity, which will promote the relevant research toward self-powered photodetection with greatly improved performance.

12.Self-driven photodetection based on impedance matching effect between a triboelectric nanogenerator and a MoS2 nanosheets photodetector

Author:Han, L;Peng, MF;Wen, Z;Liu, YN;Zhang, Y;Zhu, QQ;Lei, H;Liu, SN;Zheng, L;Sun, XH;Li, HX

Source:NANO ENERGY,2019,Vol.59

Abstract:Constructing electronic systems without an external power source is urgently required toward self-powered photodetection. In this work, we proposed a self-driven photodetection system with a MoS2 nanosheets photodetector as light intensity sensor, a vertical contact-separate mode triboelectric nanogenerator (CS-TENG) as power source, and several LEDs as alarm. The MoS2 based planar photodetector was fabricated by conventional photolithography technique and lift-off process. It is highly sensitive for visible light illumination with high current on-off ratio and excellent reproducibility characteristics under light on-off switching. When conjuncting these functional devices, the induced output voltage of the CS-TENG is tuned by the load resistance of the photodetector, which is responded to the light intensity. The mechanism can be ascribed to the impedance matching effect between specific output characteristics of TENG and working status of photodetector. By adding a Zener diode acts as a voltage regulator, the self-driven renders the voltage and current varying from 1.58 to 20.60 V and 0.06-4.78 mu A in a range of light intensity from 0 to 3.19 W/m(2), respectively. Finally, it is demonstrated that the output of CS-TENG varies with the variable working states of the MoS(2 )photodetector and then accurately reflects on the lighted number of LEDs.

13.Generalized Bernoulli Polynomials: Solving Nonlinear 2D Fractional Optimal Control Problems

Author:Hassani, H;Machado, JAT;Avazzadeh, Z;Naraghirad, E;Dahaghin, MS


Abstract:This work develops an optimization method based on a new class of basis function, namely the generalized Bernoulli polynomials (GBP), to solve a class of nonlinear 2-dim fractional optimal control problems. The problem is generated by nonlinear fractional dynamical systems with fractional derivative in the Caputo type and the Goursat-Darboux conditions. First, we use the GBP to approximate the state and control variables with unknown coefficients and parameters. Afterwards, we substitute the obtained values for the variables and parameters in the objective function, nonlinear fractional dynamical system and Goursat-Darboux conditions. The 2-dim Gauss-Legendre quadrature rule together with a fractional operational matrix construct a constrained problem, that is solved by the Lagrange multipliers method. The convergence of the GBP method is proved and its efficiency is demonstrated by several examples.

14.Absolute linear instability in laminar and turbulent gas-liquid two-layer channel flow

Author:Naraigh, LO;Spelt, PDM;Shaw, SJ


Abstract:We study two-phase stratified flow where the bottom layer is a thin laminar liquid and the upper layer is a fully developed gas flow. The gas flow can be laminar or turbulent. To determine the boundary between convective and absolute instability, we use Orr-Sommerfeld stability theory, and a combination of linear modal analysis and ray analysis. For turbulent gas flow, and for the density ratio r = 1000, we find large regions of parameter space that produce absolute instability. These parameter regimes involve viscosity ratios of direct relevance to oil and gas flows. If, instead, the gas layer is laminar, absolute instability persists for the density ratio r = 1000, although the convective/absolute stability boundary occurs at a viscosity ratio that is an order of magnitude smaller than in the turbulent case. Two further unstable temporal modes exist in both the laminar and the turbulent cases, one of which can exclude absolute instability. We compare our results with an experimentally determined flow-regime map, and discuss the potential application of the present method to nonlinear analyses.

15.Goodness of fit test for almost cyclostationary processes

Author:Mahmoudi, MR;Heydari, MH;Avazzadeh, Z;Pho, KH


Abstract:This paper is devoted to present a goodness of fit test for discrete-time almost cyclostationary models. The main strategy is based on the spectral support estimation and the application of multiple testing. The results of applying the presented method on simulated and real datasets confirm that the introduced approach acts well in view of power study. Published by Elsevier Inc.

16.Chebyshev polynomials for the numerical solution of fractal-fractional model of nonlinear Ginzburg-Landau equation

Author:Heydari, MH;Atangana, A;Avazzadeh, Z


Abstract:This paper introduces a new version for the nonlinear Ginzburg-Landau equation derived from fractal-fractional derivatives and proposes a computational scheme for their numerical solutions. The fractal-fractional derivative is defined in the Atangana-Riemann-Liouville sense with Mittage-Leffler kernel. The proposed approach is based on the shifted Chebyshev polynomials (S-CPs) and the collocation scheme. Through the way, a new operational matrix (OM) of fractal-fractional derivative is derived for the S-CPs and used in the presented method. More precisely, the unknown solution is separated into their real and imaginary parts, and then, these parts are expanded in terms of the S-CPs with undetermined coefficients. These expansions are substituted into the main equation and the generated operational matrix is utilized to extract a system of nonlinear algebraic equations. Thereafter, the yielded system is solved to obtain the approximate solution of the problem. The accuracy of the proposed approach is examined through some numerical examples. Numerical results confirm the suggested approach is very accurate to provide satisfactory results.

17.Substructure preconditioners for a class of structured linear systems of equations

Author:Zhou, JT;Niu, QA


Abstract:We proposed a substructure preconditioner for a class of structured linear system of equations. We show that a preconditioner with half of the constraint terms is able to make the preconditioned matrix have only three distinct eigenvalues. For some practical applications, a regularized variant is formulated, and the influence of the regularization parameter is analyzed. Numerical results show that the regularized variant is as efficient and is able to produce nearly optimal convergence behavior with a wide range of parameters. (C) 2010 Elsevier Ltd. All rights reserved.

18.Foreign Currency Option Pricing with Transaction Costs Driven by Fractional Brownian Motion

Author:XU Li-li;WU Zi-li

Source:Journal of Quantitative Economics,2012,Vol.29


19.Reactive Power Reduction Method Based on Harmonics Analysis for Dual Active Bridge Converters with 3-Level Modulated Phase-Shift Control

Author:Shi, HC;Wen, HQ;Chen, J


Abstract:This paper presents a novel reactive power minimization method under 3-level modulated phase-shift control in order to improve the efficiency for a wide range. Firstly a mathematic model of the DAB converter with 3-level modulated phase-shift control by a harmonic analysis method is obtained. Then, the detailed analysis of the odd order harmonic component of the active and reactive varied with the multiple control dimension is presented. On this basis, a novel optimal 3-level phase-shift control (OPS) strategy for reducing reactive power is proposed. Main simulation and experimental results by using the tradition method and the optimal reactive power reducing method are provided to verify the effectiveness of OPS method.

20.Temporal change analysis for computer aided mass detection in mammography

Author:Ma, F;Yu, LM;Liu, G;Niu, Q


Abstract:This paper presents a method to extract change information from temporal mammogram pairs and to incorporate the temporal change information in the malignant mass classification. In this method, a temporal mammogram registration framework which is based on spatial relations between regions of interest and graph matching was used to create correspondences between regions of current mammogram and regions of previous mammogram. 18 image features were then used to capture the differences (temporal changes) between the matched regions. To assess the contribution of temporl change information to the mass detection, 4 methods were designed to combine mass classification on image features measured on single regions and mass classification on temporal features to improve overall mass classification. The method was tested on 95 pairs of temporal mammograms using k-fold cross validation procedure. The experimental results showed that, when combining two classification results using linear combination or by taking minimum value, the A(z) score of overall classification performance increased from 0.8843 to 0.8958 and 0.8962 respectively. The results demonstrated that registering temporal mammograms, measuring temporal changes from matched regions and incorporating the change information in the mass classification improves the overall mass detection.
Total 112 results found
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