Decomposition of the complete graph plus a 1‐factor into cycles of equal length

We determine the necessary and sufficient conditions for the existence of a decomposition of the complete graph of even order with a 1‐factor added into cycles of equal length. © 2003 Wiley Periodicals, Inc. J Combin Designs 11: 170–207, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10019     

Existence of extremal metrics on almost homogeneous manifolds of cohomogeneity one —IV

This paper is the first of a series of papers in which we generalize our results in (Asian J. of Math. 4, 817–830 (2000); J. Geom. Anal. 12, 63–79 (2002); Intern. J. Math. 14, 259–287 (2003)) to the general complex compact almost homogeneous manifolds of real cohomogeneity one. In this paper we deal with the exceptional case of the G ₂ action (Cf. Intern. J. Math. 14, 259–287 (2003), p. 285). In particular, we prove the existence of Kähler-Einstein metric on this manifold.     

Resolvable even‐cycle systems with a 1‐rotational automorphism

In this article, necessary and sufficient conditions for the existence of a 1‐rotationally resolvable even‐cycle system of λK_v are given, which are eventually for the existence of a resolvable even‐cycle system of λK_v. © 2003 Wiley Periodicals, Inc. J Combin Designs 11: 394–407, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10058     

An algebraic characterization of projective‐planar graphs

We give a detailed algebraic characterization of when a graph G can be imbedded in the projective plane. The characterization is in terms of the existence of a dual graph G* on the same edge set as G, which satisfies algebraic conditions inspired by homology groups and intersection products in homology groups. © 2003 Wiley Periodicals, Inc. J Graph Theory 42: 320–331, 2003     

Numerical analysis of reaction front propagation model under Boussinesq approximation

This paper deals with numerical analysis of system coupling Navier–Stokes equations with two non‐linear reaction–diffusion equations. This system modelize a propagation of reaction front at the case of polymerization. A finite elements approximation is presented, the existence and uniqueness are established. Optimal error estimates are given. Copyright © 2003 John Wiley & Sons, Ltd.     

On a finite element method for unsteady compressible viscous flows

In this article we present an analysis of a finite element method for solving two‐dimensional unsteady compressible Navier‐Stokes equations. Under the time‐stepping size restriction Δt ≤ Ch, we prove the existence and uniqueness of the numerical solution and obtain an a prior error estimate uniform in time. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 152–166, 2003     

On a first‐order hyperbolic coagulation model

We consider a first‐order hyperbolic initial–boundary value problem that models coagulation of particles. We establish a comparison principle and construct monotone sequences to show the existence and uniqueness of the solution. Copyright © 2003 John Wiley & Sons, Ltd.     

On the standing wave in coupled non‐linear Klein–Gordon equations

This paper is concerned with the standing wave in coupled non‐linear Klein–Gordon equations. By an intricate variational argument we establish the existence of standing wave with the ground state. Then we derive out the sharp criterion for blowing up and global existence by applying the potential well argument and the concavity method. We also show the instability of the standing wave. Copyright © 2003 John Wiley & Sons, Ltd.     

The Milne problem for the linear Fokker–Planck operator with a force term

This paper deals with the mathematical analysis of the linear stationary Fokker–Planck equation in a half‐space (also called ‘Milne’ problem), in presence of an external electrostatic force field. We prove existence, uniqueness and asymptotic properties of the solution. Copyright © 2003 John Wiley & Sons, Ltd.     

Graph homomorphisms through random walks

In this paper we introduce some general necessary conditions for the existence of graph homomorphisms, which hold in both directed and undirected cases. Our method is a combination of Diaconis and Saloff–Coste comparison technique for Markov chains and a generalization of Haemers interlacing theorem. As some applications, we obtain a necessary condition for the spanning subgraph problem, which also provides a generalization of a theorem of Mohar (1992) as a necessary condition for Hamiltonicity. In particular, in the case that the range is a Cayley graph or an edge‐transitive graph, we obtain theorems with a corollary about the existence of homomorphisms to cycles. This, specially, provides a proof of the fact that the Coxeter graph is a core. Also, we obtain some information about the cores of vertex‐transitive graphs. © 2003 Wiley Periodicals, Inc. J Graph Theory 44: 15–38, 2003     

Rotational k‐cycle systems of order v < 3k; another proof of the existence of odd cycle systems

We give an explicit solution to the existence problem for 1‐rotational k‐cycle systems of order v < 3k with k odd and v ≠ 2k + 1. We also exhibit a 2‐rotational k‐cycle system of order 2k + 1 for any odd k. Thus, for k odd and any admissible v < 3k there exists a 2‐rotational k‐cycle system of order v. This may also be viewed as an alternative proof that the obvious necessary conditions for the existence of odd cycle systems are also sufficient. © 2003 Wiley Periodicals, Inc. J Combin Designs 11: 433–441, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10061     

Incomplete group divisible designs with block size four

The object of this paper is the construction of incomplete group divisible designs (IGDDs) with block size four, group‐type (g, h)^u and index unity. It is shown that the necessary conditions for the existence of such an IGDD are also sufficient with three exceptions and six possible exceptions. © 2003 Wiley Periodicals, Inc. J Combin Designs 11: 442–455, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jcd.10055     

On the Stochastic Strichartz Estimates and the Stochastic Nonlinear Schrödinger Equation on a Compact Riemannian Manifold

We prove the existence and the uniqueness of a solution to the stochastic NSLEs on a two-dimensional compact riemannian manifold. Thus we generalize (and improve) a recent work by Burq et al. (J Nonlinear Math Phys 10(1):12–27, 2003) and a series of papers by de Bouard and Debussche, see e.g. de Bouard and Debussche (Commun Math Phys 205(1):161–181, 1999 and Stoch Anal Appl 21(1):97–126, 2003) who have examined similar questions in the case of the flat euclidean space. We prove the existence and the uniqueness of a local maximal solution to stochastic nonlinear Schrödinger equations with multiplicative noise on a compact d-dimensional riemannian manifold. Under more regularity on the noise, we prove that the solution is global when the nonlinearity is of defocusing or of focusing type, d?=?2 and the initial data belongs to the finite energy space. Our proof is based on improved stochastic Strichartz inequalities.     

A PDE representation of the density of the minimal entropy martingale measure in stochastic volatility markets

Under general conditions stated in Rheinländer [An entropy approach to the stein/stein model with correlation. Preprint, 2003, ETH Zürich.], we prove that in a stochastic volatility market the Radon–Nikodym density of the minimal entropy martingale measure (MEMM) can be expressed in terms of the solution of a semilinear PDE. The semilinear PDE is suggested by the dynamic programming approach to the utility indifference pricing problem of contingent claims. One of our main results is the existence and uniqueness of a classical solution of the semilinear PDE in the case of a general stochastic volatility model with additive noise correlated with the asset price. Our results are applied to the Stein–Stein and Heston stochastic volatility models.     

Global existence of solutions for non‐small data to non‐linear spherically symmetric thermoviscoelasticity

We consider some initial–boundary value problems for non‐linear equations of thermoviscoelasticity in the three‐dimensional case. Since, we are interested to prove global existence we consider spherically symmetric problem. We examine the Neumann conditions for the temperature and either the Neumann or the Dirichlet boundary conditions for the elasticity equations. Using the energy method, we are able to obtain some energy estimates in appropriate Sobolev spaces enough to prove existence for all time without any restrictions on data. Due to the spherical symmetricity the constants in the above estimates increase with time so the existence for all finite times is proved only. Copyright © 2003 John Wiley & Sons, Ltd.     

On a non-homogeneous bi-layer shallow-water problem: smoothness and uniqueness results

In this paper, we present several results for a non-homogeneous bi-layer shallow-water model in depth-mean velocity formulation. The homogeneous case was studied in (Nonlinear Anal.: Real World Appl. 4(1) (2003) 139–171). In (On a non-homogeneous bi-layer shallow water problem: an existence theorem, Diff. and Integral Equations 17 (9–10) (2004) 1175–1200) we proved the existence of a solution for the non-homogeneous problem and now we give some smoothness and uniqueness results. The main difficulties in the non-homogeneous case arise from the treatment of the boundary terms.     

Global existence for the Vlasov–Darwin system in ℝ3 for small initial data

We prove the global existence of weak solutions to the Vlasov–Darwin system in R3 for small initial data. The Vlasov–Darwin system is an approximation of the Vlasov–Maxwell model which is valid when the characteristic speed of the particles is smaller than the light velocity, but not too small. In contrast to the Vlasov–Maxwell system, the total energy conservation does not provide an L2‐bound on the transverse part of the electric field. This difficulty may be overcome by exploiting the underlying elliptic structure of the Darwin equations under a smallness assumption on the initial data. We finally investigate the convergence of the Vlasov–Darwin system towards the Vlasov–Poisson system. Copyright © 2003 John Wiley & Sons, Ltd.     

Existence of strong solutions for the problem of a rigid-fluid system

This Note is devoted to the study of a fluid–rigid body interaction problem. The motion of the fluid is modelled by the Navier–Stokes equations, written in an unknown bounded domain depending on the displacement of the rigid body. Our main result yields the existence and uniqueness of strong solutions, which are global provided that the rigid body does not touch the boundary. To cite this article: T. Takahashi, C. R. Acad. Sci. Paris, Ser. I 336 (2003).