Moving boundary problem for a one-dimensional crawling nematode sperm cell model

This paper is a continuation of the authors’ investigation of the crawling nematode sperm cell model proposed by Mogilner and Verzi in 2003 (J. Stat. Phys. 110 (2003) 1169). In the earlier papers (J. Math. Biol. 49 (2004) 310 and J. Math. 8 (2004) 399), the first and last authors and Juliet Lee proved the existence of traveling wave solutions for the nematode sperm cell model. In this paper, we prove local existence of solutions to the same model and global existence under certain additional assumption on the initial data. Finally, we also provide numerical evidence that the traveling wave solutions found in (J. Math. Biol., accepted for publication) is globally asymptotically stable.     

Free boundary problem for a viscous compressible flow associated with oxidation of silicon

This paper is concerned with a free boundary problem describing the oxidation process of silicon. Its mathematical model is a compressible Navier-Stokes equations coupling a parabolic equation and a hyperbolic one. Surface tension is involved at the free boundary and density equation is non-homogeneous. It is proved that for arbitrary data satisfying only natural consistency conditions the problem is uniquely solvable on some finite time interval. Supported by National Natural Science Foundation of China     

Spectral-fractional step Runge-Kutta discretizations for initial boundary value problems with time dependent boundary conditions

In this paper we develop a technique for avoiding the order reduction caused by nonconstant boundary conditions in the methods called splitting, alternating direction or, more generally, fractional step methods. Such methods can be viewed as the combination of a semidiscrete in time procedure with a special type of additive Runge-Kutta method, which is called the fractional step Runge-Kutta method, and a standard space discretization which can be of type finite differences, finite elements or spectral methods among others. Spectral methods have been chosen here to complete the analysis of convergence of a totally discrete scheme of this type of improved fractionary steps. The numerical experiences performed also show the increase of accuracy that this technique provides.

     

Branches of positive and free boundary solutions for some singular quasilinear elliptic problems

We study the existence and multiplicity of solutions, strictly positive or nonnegative having a free boundary (the boundary of the set where the solution vanishes) of some one-dimensional quasilinear problems of eigenvalue type with possibly singular nonlinear terms.     

One-dimensional free boundary problem for actin-based propulsion of Listeria

Some bacteria move inside cells by recruiting the actin filaments of the host cells. The filaments are polymerized at the back surface of the bacteria, and they move away, forming a “comet” tail behind the bacterium, which consists of gel network. We develop a one-dimensional mathematical model of the gel based on partial differential equations which involve the number of filaments, the density and velocity of the gel, and the pressure. The two end-points of the gel form two free boundaries. The resulting free boundary problem is rather non-standard. We prove local existence and uniqueness.     

Free boundary regularity close to initial state for parabolic obstacle problem

In this paper we study the behavior of the free boundary , arising in the following complementary problem:

Here denotes the parabolic boundary, is a parabolic operator with certain properties, is the upper half of the unit cylinder in , and the equation is satisfied in the viscosity sense. The obstacle is assumed to be continuous (with a certain smoothness at , ), and coincides with the boundary data at time zero. We also discuss applications in financial markets.

     

Solution curves and exact multiplicity results for 2mth order boundary value problems

For any integer m?2, we consider the 2mth order boundary value problem

(−1)mu(2m)(x)=λg(u(x))u(x),x∈(−1,1),     

Generalized Stokes resolvent equations in an infinite layer with mixed boundary conditions

In this paper we prove unique solvability of the generalized Stokes resolvent equations in an infinite layer Ω₀ = ℝ^{n –1} × (–1, 1), n ≥ 2, in L^q ‐Sobolev spaces, 1 < q < ∞, with slip boundary condition of on the “upper boundary” ∂Ω⁺₀ = ℝ^{n –1} × {1} and non‐slip boundary condition on the “lower boundary” ∂Ω^–₀ = ℝ^{n –1} × {–1}. The solution operator to the Stokes system will be expressed with the aid of the solution operators of the Laplace resolvent equation and a Mikhlin multiplier operator acting on the boundary. The present result is the first step to establish an L^q ‐theory for the free boundary value problem studied by Beale [9] and Sylvester [22] in L ²‐spaces. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Positive solutions for a Floquet functional boundary value problem

In this paper we prove the existence of multiple positive solutions for a boundary value problem concerning a first order functional differential equation. The results are obtained by using two fixed point theorems on appropriate cones in Banach spaces. These theorems are based on the fixed point index theory.     

The generalized solution of ill-posed boundary problem

In this paper, we define a kind of new Sobolev spaces, the relative Sobolev spaces Wk,p0(Ω,∑). Then an elliptic partial differential equation of the second order with an ill-posed boundary is discussed. By utilizing the ideal of the generalized inverse of an operator, we introduce the generalized solution of the ill-posed boundary problem. Eventually, the connection between the generalized inverse and the generalized solution is studied. In this way, the non-instability of the minimal normal least square solution of the ill-posed boundary problem is avoided.     

A dynamic boundary value problem arising in the ecology of mangroves

We consider an evolution model describing the vertical movement of water and salt in a domain splitted in two parts: a water reservoir and a saturated porous medium below it, in which a continuous extraction of fresh water takes place (by the roots of mangroves). The problem is formulated in terms of a coupled system of partial differential equations for the salt concentration and the water flow in the porous medium, with a dynamic boundary condition which connects both subdomains.We study the existence and uniqueness of solutions, the stability of the trivial steady state solution, and the conditions for the root zone to reach, in finite time, the threshold value of salt concentration under which mangroves may live.     

A free boundary problem describing reaction-diffusion problems in chemical vapor infiltration of pyrolytic carbon

In this paper we consider chemical vapor deposition of pyrolytic carbon from methane in hot wall reactors. Especially, we deal with the interaction of homogeneous gas-phase and heterogeneous surface reactions. The resulting mathematical model is composed of a system of reaction-diffusion equations in a corner domain supplied with the Gibbs-Thomson law, which describes the movement of the free boundary, arising from the carbon deposition. We prove a short time existence and uniqueness result in Hölder spaces. We achieve this by contraction arguments and transforming the Gibbs-Thomson law to local coordinates to obtain a nonlinear parabolic equation on a manifold.     

Nonlinear boundary value problems for discontinuous delayed differential equations

In this paper nonlinear boundary value problems for discontinuous delayed differen- tial equations are considered. Some existence and boundedness results of solutions are obtained via the method of upper and lower solutions, which may be discontinuous. Our analysis can be applied to those phenomena from physics and control theory which have been successfully described by delayed differential equations with discontinuous functions, such as electric, pneu- matic, and hydraulic networks. It is also an important step to precede the design of control signals when finite-time or practical stability control are concerned.     

A Fully Nonlinear Boundary value Problem for the Laplace Equation in Dimension Two

We study the regularity up to the boundary of solutions to the boundary value problem:[math001] in D, ∣?u∣= g on &;pardD, where D is the unit disc. This problem finds its application in the study of geophysical and geomagnetic surveys. If g?C^,[math001](D) and is strictly positive, we prove that uis in the Holder class C1,α(D). An example shows that this is no longer true if g has some zeroes on ?D. In this case u isproved to be of class C¹(D)     

Impulsive anti-periodic boundary value problem for nonlinear differential equations of fractional order

In this paper, we prove the existence and uniqueness of solutions for an anti-periodic boundary value problem of nonlinear impulsive differential equations of fractional order α∈(2,3] by applying some well-known fixed point theorems. Some examples are presented to illustrate the main results.