Coupled surface and grain boundary motion: a travelling wave solution

Existence and uniqueness are proven for a travelling wave solution for a problem in which motion by mean curvature is coupled with surface diffusion. This problem pertains to a bicrystal in a “quarter-loop” geometry in which one grain grows at the expense of the other, and the internal grain boundary between the two crystals contacts the exterior surface at a “groove root” or “tri-junction” where various balance laws hold. Far in front and behind the groove root the overall height of the bicrystal is assumed to be unperturbed. Whereas in a previous paper (Acta Mater. 51 (2003) 1981) a partially linearized formulation was considered for which explicit solutions could be found, here we treat the fully nonlinear problem. Employing an angle formulation and a scaled arc-length parameterization, we reduce the problem to the solution of a third order ODE with a jump condition at the origin. Existence is proven if m, the ratio of the exterior surface energy to the surface energy of the grain boundary, is less than about $\approx 0.92$. Uniqueness of these solutions is demonstrated within the class of single-valued solutions. A numerical comparison is made with the solution of the partially linearized formulation found earlier for the sake of illustration.     

An integrable fourth-order nonlinear evolution equation applied to thermal grooving of metal surfaces

The fourth-order nonlinear partial differential equation forsurface diffusion is approximated by a new integrable nonlinearevolution equation. Exact solutions are obtained for thermalgrooving, subject to boundary conditions representing a sectionof a grain boundary. When the slope m of the groove centre islarge, the linear model grossly overestimates the groove depth.In the linear model dimensionless groove depth increases linearlywith m, but in the nonlinear model it approaches an upper limitA nontrivial similarity solution is found for the limiting caseof a thermal groove whose central slope is vertical.     

A 2D level set finite element grain coarsening study with heterogeneous grain boundary energies

In a previous article (Fausty et al., 2018) a new level-set finite element formulation for pure grain growth with heterogeneous grain boundary energies (i.e. one energy per grain interface) was developed and validated for simple configurations. In this work, the authors apply this new tool to the simulation of two dimensional grain growth of polycrystals using different disorientation dependent grain boundary energy functions. The results of these full-field calculations are assessed using the time dependent evolution of the following criteria: grain size, grain number, total interface energy, grain boundary disorientation distribution, grain boundary energy distribution and number of neighboring grains distribution. Of particular interest is the relationship between the grain boundary energy function and the evolution of the grain boundary network in the sense of both its morphology and its constitution. Some notable results are that the disorientation distribution evolution is inversely correlated to the grain boundary energy function itself and that the kinetics of grain growth are heavily effected by the heterogeneity of the system.     

Advection-diffusion dynamics with nonlinear boundary flux as a model for crystal growth

We analyze the effect of nonlinear boundary conditions on an advection-diffusion equation on the half-line. Our model is inspired by models for crystal growth where diffusion models diffusive relaxation of a displacement field, advection is induced by apical growth, and boundary conditions incorporate non-adiabatic effects on displacement at the boundary. The equation, in particular the boundary fluxes, possesses a discrete gauge symmetry, and we study the role of simple, entire solutions, here periodic, homoclinic, or heteroclinic relative to this gauge symmetry, in the global dynamics.     

Regularity of solutions to a free boundary problem modeling tumor growth by Stokes equation

In this paper we investigate regularity of solutions to a free boundary problem modeling tumor growth in fluid-like tissues. The model equations include a quasi-stationary diffusion equation for the nutrient concentration, and a Stokes equation with a source representing the proliferation density of the tumor cells, subject to a boundary condition with stress tensor effected by surface tension. This problem is a fully nonlinear problem involving nonlocal terms. Based on the employment of the functional analytic method and the theory of maximal regularity, we prove that the free boundary of this problem is real analytic in temporal and spatial variables for initial data of less regularity.     

Einfluss eines Verbrennungsvorganges auf den Wärme- und Stoffaustausch in einer laminaren Grenzschicht

Summary The influence of combustion on heat and mass transfer is investigated on the following model. A mixture of an inert with a combustible gas (air) flows in steady, laminar flow over a flat plate. A mass flux of gaseous fuel away from the plate surface is produced by some means. Combustion is assumed to occur with very fast reaction rate so that the process is purely controlled by diffusion and the equilibrium is assumed as very close to complete combustion. It is studied under which conditions the combustion occurs at the surface or when the flame is displaced into the boundary layer. The influence of combustion on the heat transfer from a hot gas to the plate surface is calculated, for the condition that combustion occurs at the surface.      

The effects of tumor angiogenesis factor (TAF) and tumor inhibitor factors (TIFs) on tumor vascularization: A mathematical model

A mathematical model, which examines the effects of Tumor Angiogenesis Factor (TAF) and Tumor Inhibitor Factors (TIFs) on tumor angiogenesis and predicts the onset of vascularization, is presented. The TAF and TIFs are produced within the tumor, while in the prevascular stage, by a layer of viable proliferating cancer cells on the tumor boundary. When the concentrations of TAF and TIFs have reached a critical level, they are released into the surrounding tissue. If TAF and TIFs have penetrated the tissue to the extent that they can reach the tips of the neighboring capillaries, then regulation of the formation of new blood vessels begins. The present model describes this process in three stages, and the appropriate diffusion equations for the production and secretion of TAF and TIFs are solved in spherical geometry. The concentrations of these chemical substances are monitored and the rate of growth of the capillary boundary, which moves towards the tumor surface marking the onset of vascularization, is determined.     

一类带非单调转化率的捕食-食饵模型的全局分歧

主要研究了一类带非单调转化率的捕食-食饵模型,分别以生长率a和b为分歧参数,运用度理论和分歧理论讨论了这类模型在齐次第一边界条件下全局分歧结构．     

Absence of Diffusion Through the Fractal Boundary of Two Media

We consider ideal gas diffusion through a fractal boundary between two homogeneous media. This boundary is modeled by a spatially self-similar system of folds of the interface surface between the media. This surface can have a finite volume, which is then identified with the physical volume of the boundary layer. We show that the effective diffusion coefficient of ideal molecules vanishes in this layer.     

纳米单晶与多晶铜薄膜力学行为的数值模拟研究

通过对不同温度下单晶薄膜的拉伸性能的分子动力学模拟，从微观角度揭示了温度效应对材料性能的影响. 结果表明温度效应对材料的变形机理影响很大.0K温度下由于缺乏热激活软化的影响, 粒子运动所受到的阻碍较大, 薄膜的强度较高, 塑性变形主要来自于粒子的短程滑移.温度升高，粒子的热运动加剧，屈服强度降低, 塑性变形将主要来自于大范围的位错长程扩展.多晶薄膜的模拟结果表明, 虽然其晶粒形状较为特殊, 但是它仍然遵循反Hall-Petch关系.在模拟过程中，侧向应力最大值比拉伸方向应力的最大值滞后出现.位错只会从晶界产生并向晶粒内部传播，晶粒间界滑移是多晶薄膜塑性变形的主要来源.     

2014“高教社杯”全国大学生数学建模竞赛颁奖仪式在海军航空工程学院青岛校区举行

<正>2014年12月20日,2014"高教社杯"全国大学生数学建模竞赛颁奖仪式暨工作会议在海军航空工程学院青岛校区隆重举行。全国大学生数学建模竞赛组委会主任、复旦大学李大潜院士,海军航空工程学院政委龚理华少将,山东省教育厅宋承祥副厅长,高等教育出版社林金安副总编辑,中国科学院袁亚湘院士,全国大学生数学建模竞赛组委会副主任、专家组组长、浙江大学陈叔平教授等160余人出席了颁奖仪式。颁奖仪式由全国组委会秘书长、清华大学谢金星教授主持。颁奖仪式上,学院龚理华     

2014全国大学生数学建模竞赛“高教社杯”获奖感言

<正>尊敬的各位领导、老师,亲爱的同学们:大家好!室外数九隆冬,室内春意阵阵。在这温暖如春的颁奖仪式现场,我的内心既高兴又激动。让我高兴的是,我能参加"高教社杯"全国大学生数学建模竞赛;让我激动的是,自己能作为获奖者的代表在此发言。我是来自信阳师范学院数学与信息科学学院2012级的学生程双泽,我们能获得今年的高教社杯,是和无数人的关心和帮助分不开的。所以我想真诚地对他们说声-谢谢。感谢全国数学建模竞赛组委会及所有为数学建模付出心血的领导和老师们,是你们为全国广大学子提供了一个展现自我风采的平     

Well-posedness of a dissolution-growth problem on an unbounded domain

We consider a spherical grain which may be growing by accretion or dissolving in a dilute solution of the same substance where one also has reaction and diffusion. The resulting free boundary problem is shown to be well-posed and additional regularity is obtained.     

Modelling moisture uptake in a cereal grain

auther to whom correspondence should be addressed. Email: k.landman{at}ms.unimelb.edu.au.E-mail: cpp{at}maths.soton.ac.uk Recent experimental data have revealed the spatial and temporalstructure of moisture content within a cereal grain immersedin boiling water. A simple model of the water's motion is presented,guided by the observed behaviour, which allows for nonlinear(exponential) diffusion within the grain and a constant mass-transfercoefficient to represent the pericarp on the outer surface.Numerical results are presented illustrating the close relationshipof the predictions to the experimental results, with the mass-transfercoefficient as a fitting parameter. The model is studied usingasymptotic analysis, in the limit of large activation energyin the diffusion coefficient and large mass transfer. The analysisgives insight into the three phases of the process, consistingof initial linear diffusion, linear motion of the moisture frontinto the grain, and slow filling of the grain in a relativelyuniform manner. The problem is also studied using mean-action-timeanalysis to derive simple expressions for the time for the grainto saturate.     

Numerical simulation of reaction‐diffusion telegraph systems in unbounded domains

We present a boundary element method for computing numerical solutions of the reaction‐diffusion telegraph equation in unbounded domains. This technique does not need artificial boundary conditions at the computational domain and uses a new algorithm to compute the Fourier transform, the convolution theorem, and the fact that the exact solution of the telegraph equation can be written as an integral transform in terms of the fundamental solution. We use the logistic growth model to find how the population of an organism evolves according to its growth rate. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 326–335, 2015     

The optimal pace of product updates

Some firms (e.g. Intel and Medtronics) use a time-pacing strategy for product development (PD), introducing new generations at regular intervals. If the firm adopts a fast pace (introducing frequently), it prematurely cannibalizes its old generation, incurring high development costs, while if it has a slow pace, it fails to capitalize on customer willingness-to-pay for improved technology. We develop a model to gain insight into which factors drive the pace. We consider PD cost, the diffusion rate (coefficients of innovation and imitation), the rate of margin decline, and the degree to which a new generation stimulates market growth. We find that a faster pace is generally associated with faster diffusion, a higher market growth rate and faster margin decay. Not so intuitively, we find that relatively minor differences in the development cost function can significantly impact the pace.     

一个肿瘤生长自由边界问题解的渐近性态

该文研究根据Byrne和Chaplain的思想建立的一个描述抑制物作用下无坏死核肿瘤生长的数学模型, 这个模型是一个非线性反应扩散方程组的自由边界问题. 作者运用反应扩散方程理论中的上下解方法结合自由边界问题的迭代技巧, 研究了解的渐近性态, 在营养物消耗函数f、抑制物消耗函数g和肿瘤细胞繁衍函数S的一些一般条件下,证明当常数c₁,c₂(肿瘤细胞分裂速率和营养物、抑制物扩散速率的比值)都非常小时,在一定的初边值条件下肿瘤趋于消失,在另外一些初边值条件下肿瘤半径趋于一个常数,进而时变解将趋于一个稳态解.     

On the control of diffusion processes

This paper considers the control of one-dimensional diffusion processes where one of the boundaries is inaccessible and the other is regular. Costs arise from a rate depending upon the current state and control and also from jumps from the regular boundary. The boundary condition on the future cost function at the inaccessible boundary resembles that at a reflecting boundary. Theorems on optimality are proved.     

Analysis of an elliptic-parabolic free boundary problem modelling the growth of non-necrotic tumor cord

We study a free boundary problem modelling the growth of a tumor cord in which tumor cells live around and receive nutrient from a central blood vessel. The evolution of the tumor cord surface is governed by Darcy's law together with a surface tension equation. The concentration of nutrient in the tumor cord satisfies a reaction-diffusion equation. In this paper we first establish a well-posedness result for this free boundary problem in some Sobolev-Besov spaces with low regularity by using the analytic semigroup theory. We next study asymptotic stability of the unique radially symmetric stationary solution. By making delicate spectrum analysis for the linearized problem, we prove that this stationary solution is locally asymptotically stable provided that the constant c representing the ratio between the diffusion time of nutrient and the birth time of new cells is sufficiently small.