Impulsive boundary value problems for p(t)-Laplacian’s via critical point theory

In this paper we investigate the existence of solutions to impulsive problems with a p(t)-Laplacian and Dirichlet boundary value conditions. We introduce two types of solutions, namely a weak and a classical one which coincide because of the fundamental lemma of the calculus of variations. Firstly we investigate the existence of solution to the linear problem, i.e. a problem with a fixed rigth hand side. Then we use a direct variational method and next a mountain pass approach in order to get the existence of at least one weak solution to the nonlinear problem.     

The effects of geometrical parameters on force distributions and mechanics of carbon nanotubes: A critical study

In this paper, using the continuum approximation together with Lennard–Jones potential, a new semi-analytical expression is given to evaluate the van der Waals interaction between two single-walled carbon nanotubes. Based on this expression, two new formulations are also proposed to model multi-walled carbon nanotubes. In the first one, the interactions between each pair of shells from the inner and outer tubes are summed up over all of the pairs, whereas in the second formulation, a set of correction factors are applied to convert the results of double-walled carbon nanotubes to the correlated multi-walled ones. With respect to the present formulations, extensive studies on the variations of force distributions are performed by varying nanotube geometries so that the important features of the geometrical parameters are explored. Moreover, an acceptance condition for a nanotube at rest which is to be sucked into a semi-infinite nanotube is obtained. The influence of different geometrical parameters on the acceptance condition and suction energy, two main characteristics of nanotube-based systems for applications such as drug delivery and so on, is fully demonstrated. Lastly, an interesting relation for the maximum value of suction energy in terms of geometrical parameters is also extracted in this study.     

Homogenization in L

Homogenization of deterministic control problems with L^∞ running cost is studied by viscosity solutions techniques. It is proved that the value function of an L^∞ problem in a medium with a periodic micro-structure converges uniformly on the compact sets to the value function of the homogenized problem as the period shrinks to 0. Our main convergence result extends that of Ishii (Stochastic Analysis, control, optimization and applications, pp. 305-324, Birkhäuser Boston, Boston, MA, 1999.) to the case of a discontinuous Hamiltonian. The cell problem is solved, but, as non-uniqueness occurs, the effective Hamiltonian must be selected in a careful way. The paper also provides a representation formula for the effective Hamiltonian and gives illustrations to calculus of variations, averaging and one-dimensional problems.     

Rigorous van der Waals effect on vibration characteristics of multi-walled carbon nanotubes under a transverse magnetic field

An analytical method is presented to investigate rigorous van der Waals interaction effect on vibration characteristics of multi-walled carbon nanotubes embedded in matrix under a transverse magnetic field. Each of the concentric tubes of multiwall carbon nanotubes is considered as an individual elastic shell and coupled with any two walls through a rigorous van der Waals interaction being dependent on the change of interlayer spacing and the radii of tubes. Results show that the rigorous van der Waals interaction effect makes the lowest magneto-vibration frequency of multi-walled carbon nanotubes decrease and the highest magneto-vibration frequency increase. The effect of rigorous van der Waals interaction on magneto-elastic vibrations of multi-walled carbon nanotubes is dependent on the transverse magnetic strength and the matrix constrained stiffness.     

On the discrete boundary value problem for anisotropic equation

In this paper we consider the discrete anisotropic boundary value problem using critical point theory. Firstly we apply the direct method of the calculus of variations and the mountain pass technique in order to reach the existence of at least one nontrivial solution. Secondly we derive some version of a discrete three critical point theorem which we apply in order to get the existence of at least two nontrivial solutions.     

二维可压缩油水两相渗流动边值问题的特征差分方法

可压缩可混溶油、水两相渗流动边值问题的研究,对重建盆地发育中油气资源运移、聚集的历史和评估油气资源的勘探与开发有重要的价值,其数学模型是一组非线性偶合偏微分方程组的动边值问题．本文对二维有界域的两类边值问题提出一类新的特征差分格式,应用区域变换、时间的变步长、粗细网格配套、变分形式、先验估计的理论和技巧,得到了最佳阶l2误差估计结果．将J．Douglas,Jr．提出的著名方法,成功地拓广到这一新领域,并得到实质性进展．它对这一领域的模型分析,数值方法和软件研制均有重要的价值．     

Geometric polyhedral models for nanotubes comprising hexagonal lattices

Two new models for the geometric structure of nanotubes comprising hexagonal lattices are described. The existing models for nanotubes typically involve rolled up planar sheets and ignore discrepancies due to curvature. The first of the models presented here assumes that all atomic locations are equidistant from the tube axis which applies for single species nanotubes such as carbon nanotubes. This model assumes that all bond angles and all bond lengths are equal in the cylindrical state, and that all atoms are equidistant from the tube axis, and from these three assumptions, expressions are given for the major geometric parameters. The second model extends this notion to tubes where all the atomic locations are not equidistant from the tube axis, which may be employed to model nanotubes comprising two chemical species that bond into a hexagonal lattice such as boron nitride nanotubes. In the second model, all bond lengths are taken to be equal and the atoms of the same species are taken to be equidistant from the tube axis, and the nanotube is assumed to comprise two species and thus there may be two radii. Fundamental to both models is the determination of a solution of a transcendental equation. Here we present a new formal Lagrange expansion of the solution. Previously given asymptotic series expansions of the exact formulae for both models lead to the conventional expressions as the leading order term. Although the correction terms are typically small, knowledge of the precise structure may be critical to comprehending many nanoscale phenomena. The new models also give rise to an expression for the wall thickness, an important geometric parameter for which at present no reliable information is available.     

Optimal synchronization of two different in‐commensurate fractional‐order chaotic systems with fractional cost function

This article investigates the optimal synchronization of two different fractional‐order chaotic systems with two kinds of cost function. We use calculus of variations for minimizing cost function subject to synchronization error dynamics. We introduce optimal control problem to solve fractional Euler–Lagrange equations. Optimal control signal and minimum time of synchronization are obtained by proposed method. Examples show the optimal synchronization of two different systems with two different cost functions. First, we use an ordinary integer cost function then we use a fractional‐order cost function and comparing the results. Finally, we suggest a cost function which has the optimal solution of this problem, and we can extend this solution to solve other synchronization problems. © 2016 Wiley Periodicals, Inc. Complexity 21: 401–416, 2016     

Pseudospectral Legendre-based optimal computation of nonlinear constrained variational problems

It is well known that, spectrally accurate solution can be maintained if the grids on which a nonlinear physical problem is to be solved must be obtained by spectrally accurate techniques. In this paper, the pseudospectral Legendre method for general nonlinear smooth and nonsmooth constrained problems of the calculus of variations is studied. The technique is based on spectral collocation methods in which the trajectory, x(t), is approximated by the Nth degree interpolating polynomial, using Legendre-Gauss-Lobatto points as the collocation points, and Lagrange polynomials as trial functions. The integral involved in the formulation of the problem is approximated based on Legendre-Gauss-Lobatto integration rule, thereby reducing the problem to a nonlinear programming one to which existing well-developed algorithms may be applied. The method is easy to implement and yields very accurate results. Illustrative examples are included to confirm the convergence of the pseudospectral Legendre method. Moreover, a numerical experiment (on a nonsmooth problem) indicates that by applying a smoothing filter procedure to the pseudospectral Legendre approximation, one can recover the nonsmooth solution within spectral accuracy.     

Generic existence of Lipschitzian solutions of optimal control problems without convexity assumptions

The Tonelli existence theorem in the calculus of variations and its subsequent modifications were established for integrands f which satisfy convexity and growth conditions. In this paper we consider a large class of optimal control problems which is identified with a complete metric space of integrands without convexity assumptions and show that for a generic integrand the corresponding optimal control problem possesses a unique solution and this solution is Lipschitzian.     

关于变分学中逆问题的研究

本文研究了变分学中的逆问题.通过变积概念的引入,给出了系统地研究变分学中逆问题的一种新途径.将这种方法应用于线弹性动力学和粘性流体力学中,建立了各自的变分原理和广义变分原理.     

Modification of upwind finite difference fractional step methods by the transient state of the semiconductor device

The mathematical model of the three‐dimensional semiconductor devices of heat conduction is described by a system of four quasi‐linear partial differential equations for initial boundary value problem. One equation of elliptic form is for the electric potential; two equations of convection‐dominated diffusion type are for the electron and hole concentration; and one heat conduction equation is for temperature. Upwind finite difference fractional step methods are put forward. Some techniques, such as calculus of variations, energy method multiplicative commutation rule of difference operators, decomposition of high order difference operators, and the theory of prior estimates and techniques are adopted. Optimal order estimates in L² norm are derived to determine the error in the approximate solution.© 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2008     

Optimization approach for data allocation in multidisk database

In the last decade, many parallel process mechanisms have been developed in information systems for enhancing their performance. But I/O throughput rates are still the bottleneck for data processing in the systems. In particular, relational database systems encounter this performance problem dealing with expensive operations such as the join operation. To treat a class of two-way join problems in database, Rotem et al. proposed a linearization method for finding the optimal allocation of relations to multidisk database such that the expected query cost is minimized. For the multidisk allocation problem with N relations and M disks, their model needs MN+N(N−1)/2+MN(N−1)/2 0–1 variables. This paper proposes a concise method to reformulate the same problem, which requires only MN+N(N−1)/2 0–1 variables. The problem can hence be more efficiently solved by the concise method. The analytical superiority of the concise method in terms of the number of iterations and execution times can be seen, through a computational experiment conducted on a set of generated test examples.     

Leitmann’s direct method of optimization for absolute extrema of certain problems of the calculus of variations on time scales

The fundamental problem of the calculus of variations on time scales concerns the minimization of a delta-integral over all trajectories satisfying given boundary conditions. This includes the discrete-time, the quantum, and the continuous/classical calculus of variations as particular cases. In this note we follow Leitmann’s direct method to give explicit solutions for some concrete optimal control problems on an arbitrary time scale.     

A fractional partial differential equation based multiscale denoising model for texture image

Traditional integer‐order partial differential equation based image denoising approach can easily lead edge and complex texture detail blur, thus its denoising effect for texture image is always not well. To solve the problem, we propose to implement a fractional partial differential equation (FPDE) based denoising model for texture image by applying a novel mathematical method—fractional calculus to image processing from the view of system evolution. Previous studies show that fractional calculus has some unique properties that it can nonlinearly enhance complex texture detail in digital image processing, which is obvious different with integer‐order differential calculus. The goal of the modeling is to overcome the problems of the existed denoising approaches by utilizing the aforementioned properties of fractional differential calculus. Using classic definition and property of fractional differential calculus, we extend integer‐order steepest descent approach to fractional field to implement fractional steepest descent approach. Then, based on the earlier fractional formulas, a FPDE based multiscale denoising model for texture image is proposed and further analyze optimal parameters value for FPDE based denoising model. The experimental results prove that the ability for preserving high‐frequency edge and complex texture information of the proposed fractional denoising model are obviously superior to traditional integral based algorithms, as for texture detail rich images. Copyright © 2013 John Wiley & Sons, Ltd.     

Strategic behavior in queues with the effect of the number of customers behind

In this paper, we investigate the strategic behavior in queues by considering the effect of the number of customers behind. The equilibrium joining strategy of customers is obtained and its implications for the service system are examined. We find that the complete queue transparency (i.e., disclosing the real-time system information) can have positive effect on customers, which might encourage more customers to join. Further, the follow-the-crowd (FTC) behavior can be observed, which results in multiple equilibria. By comparing the customer welfare under two different information levels, we demonstrate that, somewhat surprisingly, the queue transparency does not necessarily hurt the customer welfare, and a higher customer welfare can be obtained in the transparent case than that in opaque case when the demand volume is large.     

Non-convex self-dual Lagrangians: New variational principles of symmetric boundary value problems

We study the concept and the calculus of Non-convex self-dual (Nc-SD) Lagrangians and their derived vector fields which are associated to many partial differential equations and evolution systems. They indeed provide new representations and formulations for the superposition of convex functions and symmetric operators. They yield new variational resolutions for large class of Hamiltonian partial differential equations with variety of linear and nonlinear boundary conditions including many of the standard ones. This approach seems to offer several useful advantages: It associates to a boundary value problem several potential functions which can often be used with relative ease compared to other methods such as the use of Euler-Lagrange functions. These potential functions are quite flexible, and can be adapted to easily deal with both nonlinear and homogeneous boundary value problems. Additionally, in most cases the solutions generated using this new method have greater regularity than the solutions obtained using the standard Euler-Lagrange function. Perhaps most remarkable, however, are the permanence properties of Nc-SD Lagrangians; their calculus is relatively manageable, and their applications are quite broad.     

Formulation of Euler-Lagrange equations for fractional variational problems

This paper presents extensions to traditional calculus of variations for systems containing fractional derivatives. The fractional derivative is described in the Riemann-Liouville sense. Specifically, we consider two problems, the simplest fractional variational problem and the fractional variational problem of Lagrange. Results of the first problem are extended to problems containing multiple fractional derivatives and unknown functions. For the second problem, we also present a Lagrange type multiplier rule. For both problems, we develop the Euler-Lagrange type necessary conditions which must be satisfied for the given functional to be extremum. Two problems are considered to demonstrate the application of the formulation. The formulation presented and the resulting equations are very similar to those that appear in the field of classical calculus of variations.     

A posteriori error estimation for nonlinear variational problems

We introduce a new modus operandi for a posteriori error estimation for nonlinear (and linear) variational problems based on the duality theory of the calculus of variations. We derive what we call duality error estimates and show that they yield computable a posteriori error estimates without directly solving the dual problem.     

A variational theory for hight rays on Lorentz manifolds

The aim of this Note is the study of light rays that join an event p with a timelike curve γ in a light-convex open subset Λ of a stably causal Lorentzian manifold M. We present an intrinsic approach to the Theory of Ljusternik and Schnirelman and to the Morse Theory in the space of H^1,2 -lightlike curves joining p and γ. The theory may give a mathematical model for the so called gravitational lensing effect in astrophysics.