A Riemannian metric is said to be Einstein if the Ricci curvature is a constant multiple of the metric. Given a manifold M , one can ask whether M carries an Einstein metric, and if so, how many. This fundamental question in Riemannian geometry is for the most part unsolved (cf. [Bes]). As a global PDE or a variational problem, the question is intractible. It becomes more manageable in the homo...

Let N be a simply connected nilpotent Lie group and let S = N o (R+)d be a semidirect product, (R+)d acting on N by diagonal automorphisms. Let (Qn, Mn) be a sequence of i.i.d. random variables with values in S. Under natural conditions, including contractivity in the mean, there is a unique stationary measure ν on N for the Markov process Xn = MnXn−1 + Qn. We prove that for an appropriate homo...

The present work considers (4+1)-dimensional spatially homogeneous vacuum cosmological models. Exact solutions — some already existing in the literature, and others believed to be new — are exhibited. Some of them are the most general for the corresponding Lie group with which each homogeneous slice is endowed, and some others are quite general. The characterization " general " is given based o...

We consider natural Hamiltonian systems of n > 1 degrees of freedom with polynomial homogeneous potentials of degree k. We show that under a genericity assumption, for a fixed k, at most only a finite number of such systems is integrable. We also explain how to find explicit forms of these integrable potentials for small k.

In this paper we will prove that if $L$ is a continuous symmetric n-linear form on a Hilbert space and $widehat{L}$ is the associated continuous n-homogeneous polynomial, then $||L||=||widehat{L}||$. For the proof we are using a classical generalized  inequality due to S. Bernstein for entire functions of exponential type. Furthermore we study the case that if X is a Banach space then we have t...

It is shown that a homogeneous set of n points in the d-dimensional Euclidean space determines at least Ω(n2d/(d 2+1)/ log n) distinct distances for a constant c(d) > 0. In three-space, the above general bound is slightly improved and it is shown that a homogeneous set of n points determines at least Ω(n.6091) distinct distances.

Let N , N1 and N2 be point processes such that N1 is obtained from N by homogeneous independent thinning and N2 = N −N1. We give a new elementary proof that N1 and N2 are independent if and only if N is a Poisson point process. We present some applications of this result to test if a homogeneous point process is a Poisson point process.

Chondrocytes are the living cells in articular cartilage (AC). They synthesize and maintain the extracellular matrix. Their activity is regulated by the interplay of genetic and environmental factors, such as soluble mediators, extracellular matrix composition, and mechanical factors. The mechanical environment of the chondrocytes has a significant influence on the health of the joint. In past ...

In the present paper, an asymptotic model is constructed for the short-time deformation of an articular cartilage layer modeled as transversely isotropic, transversely homogeneous (TITH) biphasic material. It is assumed that the layer thickness is relatively small compared with the characteristic size of the normal surface load applied to the upper surface of the cartilage layer, while the bott...