It is shown that the adjoint group ${{R}^{{}^\circ }}$ of an arbitrary radical ring $R$ has a series with abelian factors and that its finite subgroups are nilpotent. Moreover, some criteria for subgroups of ${{R}^{{}^\circ }}$ to be locally nilpotent are given.

Let $K$ be a convex body in ${{\mathbf{E}}^{d}}$ and denote by ${{C}_{n}}$ the set of centroids of $n$ non-overlapping translates of $K$. For $\varrho \,>\,0$, assume that the parallel body conv ${{C}_{n}}\,+\,\varrho K$ of conv ${{C}_{n}}$ has minimal volume. The notion of parametric density (see [21]) provides a bridge between finite and infinite packings (see [4] or [14]). It is known that there exists a maximal ${{\varrho }_{s}}(K)\,\ge \,1/(32{{d}^{2}})$ such that conv ${{C}_{n}}$ is a segment for $\varrho \,<\,{{\varrho }_{s}}$ (see [5]). We prove the existence of a minimal ${{\varrho }_{c}}(K)\,\le \,d\,+\,1$ such that if $\varrho \,>\,{{\varrho }_{c}}$ and $n$ is large then the shape of conv ${{C}_{n}}$ can not be too far from the shape of $K$. For $d\,=\,2$, we verify that ${{\varrho }_{s\,}}\,=\,{{\varrho }_{c}}$. For $d\,\ge \,3$, we present the first example of a convex body with known ${{\varrho }_{s}}$ and ${{\varrho }_{c}}$; namely, we have ${{\varrho }_{s}}\,=\,{{\varrho }_{c}}\,=\,1$ for the parallelotope.

Given function $\Omega $ on ${{\mathbb{R}}^{n}}$, we define the fractional maximal operator and the fractional integral operator by

$${{M}_{\Omega ,\,\alpha }}f(x)\,=\,_{r>0}^{\sup }\frac{1}{{{r}^{n-\alpha }}}\,\int{{{_{|y|}}_{<r}}\,}|\Omega (y)|\,|f(x-y)|\,dy$$

$${{T}_{\Omega ,\,\alpha }}f(x)\,=\,\int{_{{{\mathbb{R}}^{n}}}}\,\frac{\Omega (y)}{{{\left| y \right|}^{n-\alpha }}}f(x-y)dy$$

$0\,<\,\alpha \,<\,n$

${{M}_{\Omega ,\,\alpha }}$

${{T}_{\Omega ,\,\alpha }}$

$\alpha ,\,s$

$A(p,\,\,q)$

$\Omega \,\in \,{{L}^{s}}({{S}^{n-1}})(s>1)$

The aim of the present paper is the computation of Green's functions for the powers ${{\mathbf{\Delta }}^{m}}$ of the invariant Laplace operator on rank-one Hermitian symmetric spaces. Starting with the noncompact case, the unit ball in ${{\mathbb{C}}^{d}}$, we obtain a complete result for $m\,=\,1,\,2$ in all dimensions. For $m\,\ge \,3$ the formulas grow quite complicated so we restrict ourselves to the case of the unit disc $(d\,=\,1)$ where we develop a method, possibly applicable also in other situations, for reducing the number of integrations by half, and use it to give a description of the boundary behaviour of these Green functions and to obtain their (multi-valued) analytic continuation to the entire complex plane. Next we discuss the type of special functions that turn up (hyperlogarithms of Kummer). Finally we treat also the compact case of the complex projective space ${{\mathbb{P}}^{d}}$ (for $d\,=\,1$, the Riemann sphere) and, as an application of our results, use eigenfunction expansions to obtain some new identities involving sums of Legendre $(d\,=\,1)$ or Jacobi $(d\,>\,1)$ polynomials and the polylogarithm function. The case of Green's functions of powers of weighted (no longer invariant, but only covariant) Laplacians is also briefly discussed.

The fundamental lemma in the theory of automorphic forms is proven for the (quasi-split) unitary group $U(3)$ in three variables associated with a quadratic extension of $p$-adic fields, and its endoscopic group $U(2)$, by means of a new, elementary technique. This lemma is a prerequisite for an application of the trace formula to classify the automorphic and admissible representations of $U(3)$ in terms of those of $U(2)$ and base change to $\text{GL(3)}$. It compares the (unstable) orbital integral of the characteristic function of the standard maximal compact subgroup $K$ of $U(3)$ at a regular element (whose centralizer $T$ is a torus), with an analogous (stable) orbital integral on the endoscopic group $U(2)$. The technique is based on computing the sum over the double coset space $T\backslash G/K$ which describes the integral, by means of an intermediate double coset space $H\backslash G/K$ for a subgroup $H$ of $G=U(3)$ containing $T$. Such an argument originates from Weissauer's work on the symplectic group. The lemma is proven for both ramified and unramified regular elements, for which endoscopy occurs (the stable conjugacy class is not a single orbit).

Generalizing the notion of invariant subspaces on the 2-dimensional torus ${{T}^{2}}$, we study the structure of ${{A}_{\phi }}$-invariant subspaces of ${{L}^{2}}({{T}^{2}})$. A complete description is given of ${{A}_{\phi }}$-invariant subspaces that satisfy conditions similar to those studied by Mandrekar, Nakazi, and Takahashi.

We prove that all Liouville's tori generic bifurcations of a large class of two degrees of freedom integrable Hamiltonian systems (the so called Jacobi–Moser–Mumford systems) are nondegenerate in the sense of Bott. Thus, for such systems, Fomenko's theory [4] can be applied (we give the example of Gel'fand–Dikii's system). We also check the Bott property for two interesting systems: the Lagrange top and the geodesic flow on an ellipsoid.

This paper considers the rational system ${{P}_{n}}({{a}_{1}},{{a}_{2}},...,{{a}_{n}})\,\,:=\,\left\{ \frac{P(x)}{\Pi _{k=1}^{n}(x-{{a}_{k}})},\,P\,\in \,{{P}_{n}} \right\}$ with nonreal elements in $\left\{ {{a}_{k}} \right\}_{k=1}^{n}\,\subset \,\mathbb{C}\,\backslash \,[-1,\,1]$ paired by complex conjugation. It gives a sharp (to constant) Markov-type inequality for real rational functions in ${{P}_{n}}({{a}_{1}},{{a}_{2}},...,{{a}_{n}})$. The corresponding Markov-type inequality for high derivatives is established, as well as Nikolskii-type inequalities. Some sharp Markov- and Bernstein-type inequalities with curved majorants for rational functions in ${{P}_{n}}({{a}_{1}},{{a}_{2}},...,{{a}_{n}})$ are obtained, which generalize some results for the classical polynomials. A sharp Schur-type inequality is also proved and plays a key role in the proofs of our main results

Iwahori-Hecke algebras for the infinite series of complex reflection groups $G(r,\,p,\,n)$ were constructed recently in the work of Ariki and Koike [AK], Broué and Malle [BM], and Ariki [Ari]. In this paper we give Murnaghan-Nakayama type formulas for computing the irreducible characters of these algebras. Our method is a generalization of that in our earlier paper [HR] in which we derived Murnaghan-Nakayama rules for the characters of the Iwahori-Hecke algebras of the classical Weyl groups. In both papers we have been motivated by C. Greene [Gre], who gave a new derivation of the Murnaghan-Nakayama formula for irreducible symmetric group characters by summing diagonal matrix entries in Young's seminormal representations. We use the analogous representations of the Iwahori-Hecke algebra of $G(r,\,p,\,n)$ given by Ariki and Koike [AK] and Ariki [Ari].

We study the intertwining operator and $h$-harmonics in Dunkl's theory on $h$–harmonics associated with reflection groups. Based on a biorthogonality between the ordinary harmonics and the action of the intertwining operator $V$ on the harmonics, the main result provides a method to compute the action of the intertwining operator $V$ on polynomials and to construct an orthonormal basis for the space of $h$-harmonics.

In this paper, we determine when two simple generalized Cartan type $W$ Lie algebras ${{W}_{d}}(A,\,T,\,\varphi )$ are isomorphic, and discuss the relationship between the Jacobian conjecture and the generalized Cartan type $W$ Lie algebras.