一类广义扩散模型解的存在性

通过考虑具二阶导数项的Landau-Ginzburg自由能量泛函,本文导出了一类广义扩散模型,进而采用经典的能量估计方法和对所引入的能量泛函进行精细的分析,获得了所论模型解的存在性和唯一性.     

中厚度复合材料夹芯层板变分渐近精细模型

为准确预测对中厚度复合材料夹芯层板分层开裂至关重要的沿厚向应力/应变分布,利用板固有小参数将原三维板分析严格拆分为沿厚向的一维分析和二维板非线性分析,并将原三维能量渐近扩展为系列二维近似能量泛函;通过对近似能量泛函中主导变分项(含翘曲项)的渐近修正,得到与原三维模型尽可能接近的近似能量,从而构建无需任何场变量假设的精细模型,并转换为工程常用的Reissner模型形式．通过4层复合材料夹芯板柱形弯曲算例表明:基于所构建模型重构的三维场精度较一阶剪切变形理论和经典层合理论更好,与精确解基本一致;由于所构建的变分渐近模型为等效单层板模型,在保证足够精度的前提下,相比三维有限元计算可减少2~3阶计算量,在精确性和有效性间取得较好的折衷．     

一个物体运动的优化模型及应用

建立了一类具广泛应用价值的物体运动非线性泛函优化模型,包括目标泛函,决策函数,约束条件,可行函数空间.决策函数是能量消耗分配函数,可行函数空间中的能量消耗分配函数确定目标泛函值,该模型的最优解是使目标泛函值最大的能量分配函数.这个非线性泛函优化模型,表述了一类物体运动能量转化为机械功的实际问题.例如机动车行驶中如何控制燃料消耗方式,使燃油消耗最少.运动员在赛跑中如何分配体能消耗使成绩最好等.该文从非线性泛函变分及优化理论角度对该模型进行了定量探讨.所得结果可应用于物体运动功能转化相关实际问题中.该文也提出了若干公开问题.     

R^N上一类Kirchhoff型方程径向对称正解的存在性

该文讨论了一类能量泛函不属于C^1类的Kirchhoff型方程,这类方程与等离子体物理和激光传输理论有密切的联系.通过变量变换,该文首先将所讨论的方程变成了与之等价的能量泛函属于C^1类的方程.然后,通过构造合适的Banach空间,在适当的条件下运用变分方法证明了所讨论的方程存在径向对称正解.     

含极限次临界增长项p-Laplace方程的无穷多解

讨论了有界光滑区域上一类p-Laplace方程,非线性项具奇对称性且在无穷远为极限次临界增长．证明了变分泛函在大范围内满足推广的Palais-Smale条件,构造了变分泛函的一列临界值,进而得到了无穷多个弱解的存在性,对应泛函的能量趋于正无穷．所得到的结果推广了次临界增长的情形．     

The Legendre Collocation Spectral Method for the Ground State Solutions of the Bose-Einstein Condensates北大核心CSCD

近年来,有关Bose-Einstein凝聚态基态解的实验研究已经取得了一系列重要的成果.该文在相关研究成果的基础上,首先通过降维和无量纲化方法将Bose-Einstein凝聚态基态解问题转换成能量泛函极值问题,在离散该泛函时,尝试使用Legendre配置谱方法离散该能量泛函的一维和二维情形.其次,对该能量泛函极小值问题进行了数值模拟.最后,通过分析实验数据结果和图像得出,针对非旋转的Bose-Einstein凝聚态的基态解问题可以使用Legendre配置谱方法来求解,且数值结果的误差较小.     

测地线活动轮廓模型的图像分割快速算法

从最优化理论的角度来看,目前求解图像分割的测地线活动轮廓(geodesic active contour,GAC)模型大多采用固定步长的最速下降算法.而众所周知,该算法收敛速度较慢,这在能量泛函的梯度较小时尤为明显.对求解GAC模型的快速算法进行了研究.首先,回顾了GAC模型的演化方程;随后,将共轭梯度(conjugate gradient,CG)算法引入到GAC模型的求解中,形成一种新的求解图像分割问题的数值方法,即GAC模型的CG算法;最后,通过试验对比传统的数值方法,表明CG算法具有良好的收敛性.     

强关联多电子体系的优化模型与算法

在电子结构计算领域,Kohn-Sham方程是最为广泛使用的数学模型之一.然而,由于现有的交换关联能近似仍存在缺陷,Kohn-Sham方程无法较好地描述强关联多电子体系.近年来,有学者从密度泛函理论的强相关极限出发,提出了严格关联电子能量的优化模型.该模型有望弥补Kohn-Sham方程的缺陷,从而拓宽密度泛函理论的应用面.由于在该模型中存在维数灾难,近年来,它的一些低维转化模型陆续被提出.在本文中,我们将介绍严格关联电子能量的优化模型、它的研究重点以及现有的一些低维转化模型.我们也将介绍这些转化模型的数值求解方法,并探讨未来的研究方向.     

带有凸和局部Lipschitz势函数的周期边值问题解的存在性(英文)

本文主要研究了带有凸和局部Lipschitz势函数的二阶周期微分包含解的存在性.通过对势函数合理的假设,利用非光滑的最小作用定理验证了由凸和局部Lipschitz泛函构成的能量泛函非光滑的PS-条件,以及能量泛函广义临界点的存在性.     

具记忆和变时滞项的二阶发展方程能量衰减率的凸性估计

研究了如下一类具有记忆和变时滞项的抽象发展方程u_(tt)(t)+Au(t)-(∫_0~t g(t-s)Au(s)ds+μ_1h_1(u_t(t))+μ_2h_2(u_t(x,t-T(t)))=▽F(u(t)).通过构造合适的能量泛函和Lyapunov泛函,利用凸函数的一些性质,得到了依赖于h_1及记忆核g的能量衰减估计.此衰减估计可以应用于一些具体的模型.     

An adaptive weighting parameter estimation between local and global intensity fitting energy for image segmentation

Local and global intensity fitting energy are widely used for image segmentation. In order to improve the segmentation quality in the presence of intensity inhomogeneity, in this paper, we propose a new adaptive rule for obtaining weighting parameter estimation between the local and global intensity fitting energy. Following the minimization of the energy functional, the value of the weighting parameter is dynamically updated with the contour evolution, which is effective and accurate for extracting the object.     

Quasineutral limit of the viscous quantum hydrodynamic model for semiconductors

The quasineutral limit (zero-Debye-length limit) of viscous quantum hydrodynamic model for semiconductors is studied in this paper. By introducing new modulated energy functional and using refined energy analysis, it is shown that, for well-prepared initial data, the smooth solution of viscous quantum hydrodynamic model converges to the strong solution of incompressible Navier-Stokes equations as the Debye length goes to zero.     

MITC元的分析

1 引言 有限元求解厚薄板通用的R-M(Reissner-Mindlin)模型板问题,单元只需具有C°连续性,这一点优于需具有C~1连续性的Kirchhoff模型薄板单元.但是当板厚趋于零时,通常的低阶C°元却不收敛,这就是所谓的Locking现象.Bathe和Brezzi等将R-M板模型转化成2阶椭园问题与Stokes问题的耦合形式,据此提出求解R-M板问题的混合扦值单元MITC~([1]、[2]、[3]):设挠度ω的形函数空间是W,转角β=(βx,βy)的形空间是B,在计算剪切应变时,分别将βx,βy按不同方式投影到空间和.数值结果表明这类单元具有很好的收敛性.本文分析MITC元,导出投影算子的显表达式,根据[5]关于Locking现象的一个数学分析,证明当板厚趋于零时,投影算子的选取方式使剪切应变部分对应于特定点上的Kirchhoff条件,引起Locking现象的因素被消除,从而显式证明MITC元避免了Locking 现象. 2 MITC元的整体性质 考虑R-M板弯曲问题,求挠度,转角,使下列板的能量泛函达极小: (1) (2) 其中E是杨氏模量,υ是Possion比,0<υ<1/2,t是板厚,k是剪力校正因子,Ω是板的中面占有的平面区域,f是横向荷载.(1)的第一项是弯曲应变能,第二项是剪切应变能. 设有限元空间是W_h×B_h,W_hH_0~1(Ω),B_h[H_0~1(Ω)]~2,J_h是Ω的单元部分,Ω=K,K是单元,对(1)的直接离散是求(     

绿色建筑前期设计阶段的多目标优化及多属性决策模型

综合考虑建筑物的体型参数、围护结构参数和功能布局的影响,运用层次分析法将描述性的功能目标转化为定量值,建立绿色建筑前期设计阶段的能耗、成本和功能的多目标优化模型。针对模型变量的离散性,以邻域拓扑结构改进粒子群算法,防止陷入局部最优,得到绿色建筑方案的Pareto解集。在绿色建筑多属性决策中引入马氏距离与组合赋权方法,对最优方案进行排序决策。通过案例分析验证该模型的效果,在保证一定功能的前提下,可获得较低的能耗和成本,实现绿色建筑设计理念。     

Exponential decay rate of a nonlinear suspension bridge model by a local distributed and boundary dampings

In this paper, we investigate the decay properties of the unconstrained one dimensional suspension bridge model. With only partial damping acting on one or on both equations and with boundary dampings, we prove that the first order energy is decaying exponentially, our method of proof is based on the energy method to build the appropriate Lyapunov functional. Moreover, we develop a numerical algorithm which is based on the finite element method to approximate the spatial variable and the Crank–Nicolson type of symmetric difference scheme to discretize the time derivative, and also a Picard type iteration process for solving the system of nonlinear equations obtained by discretization. At the end, we present some numerical experiments to illustrate our theoretical results.     

An energy functional for Lagrangian tori in $$\mathbb {C}P^2$$

A two-dimensional periodic Schrödingier operator is associated with every Lagrangian torus in the complex projective plane \({\mathbb C}P^2\). Using this operator, we introduce an energy functional on the set of Lagrangian tori. It turns out this energy functional coincides with the Willmore functional \(W^{-}\) introduced by Montiel and Urbano. We study the energy functional on a family of Hamiltonian-minimal Lagrangian tori and support the Montiel–Urbano conjecture that the minimum of the functional is achieved by the Clifford torus. We also study deformations of minimal Lagrangian tori and show that if a deformation preserves the conformal type of the torus, then it also preserves the area, i.e., preserves the value of the energy functional. In particular, the deformations generated by Novikov–Veselov equations preserve the area of minimal Lagrangian tori.     

THE PLATEAU-B(E)ZIER PROBLEM WITH WEAK-AREA FUNCTIONAL

In this paper, we present a new method to solve the Plateau-Bézier problem. A new energy functional called weak-area functional is proposed as the objective functional to obtain the approximate minimal Bézier surface from given boundaries. This functional is constructed based on Dirichlet energy and weak isothermal parameterization condition. Experimental comparisons of the weak-area functional method with existing Dirichlet, quasi-harmonic, the strain energy-minimizing, harmonic and biharmonic masks are performed which show that the weak-area functional method are among the best by choosing appropriate parameters.     

Cell membranes,Lipid Bilayers,and the Elastica Functional

We study an energy functional that arises in a simplified two-dimensional model for lipid bilayer membranes. We demonstrate that this functional, defined on a class of spatial mass densities, favours concentrations on ‘thin structures’. Stretching, fracture and bending of such structures all carry an energy penalty. In this sense we show that the models captures essential features of lipid bilayers, namely partial localisation and a solid-like behaviour. Our findings are made precise in a Gamma-convergence result. We prove that a rescaled version of the energy functional converges in the ‘zero thickness limit’ to a functional that is defined on a class of planar curves. Finiteness of the limit value enforces both optimal thickness and non-fracture; if these conditions are met, then the value of this functional is given by the classical Elastica (bending) energy. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Near boundary vortices in a magnetic Ginzburg-Landau model: Their locations via tight energy bounds

Given a bounded doubly connected domain G⊂R², we consider a minimization problem for the Ginzburg-Landau energy functional when the order parameter is constrained to take S¹-values on ∂G and have degrees zero and one on the inner and outer connected components of ∂G, correspondingly. We show that minimizers always exist for 0<λ<1 and never exist for λ?1, where λ is the coupling constant ( is the Ginzburg-Landau parameter). When λ→1−0 minimizers develop vortices located near the boundary, this results in the limiting currents with δ-like singularities on the boundary. We identify the limiting positions of vortices (that correspond to the singularities of the limiting currents) by deriving tight upper and lower energy bounds. The key ingredient of our approach is the study of various terms in the Bogomol'nyi's representation of the energy functional.