Boundary observability for the space-discretizations of the 1 — d wave equation

We consider the finite-difference and finite-element space discretization of the 1 — d wave equation with homogeneous Dirichlet boundary conditions in a bounded interval. We analyze the problem of estimating the total energy of solutions in terms of the energy concentrated on the boundary, uniformly as the net-spacing h → 0. We prove that there is no such a uniform bound due to spurious high frequencies. We prove however an uniform bound in suitable subspaces of solutions that eventually cover the whole energy space.     

Tensor invariants of the Lie algebra sl2(ℂ[t]) and fundamental representations of the Lie algebras\hat p_{2n}

Generators of the space of tensor invariants of the Lie algebra Sl₂([t]) are constructed. It is proved that the restrictions of a spinor representation of the affine Lie algebra to and form a dual pair. A realization of the fundamental representations of the Lie algebra is obtained.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova, Akad. Nauk SSSR, Vol. 172, pp. 137–144, 1989.     

Criterion for the Denseness of Algebraic Polynomials in the Spaces $$L_p \left( {{\mathbb{R}},d {\mu }} \right)$$ , 1 ≤ p < ∞

The criterion for the denseness of polynomials in the space established by Hamburger in 1921 is extended to the spaces , 1 p < .     

Hölder estimates for the\bar \partial - equation in some domains of finite typein some domains of finite type

We obtain Hölder estimates for the $\bar \partial - equation$ on some domains of finite type in ?ⁿ using proper mapping techniques. The domains considered are domains of finite type in the sense of D’Angelo and are defined by local coordinate expressions satisfying certain algebraic geometric conditions which prevent the existence of complex analytic varieties in the boundary of the domain. Using a proper mapping which is given by the finite type condition and which carries all the information about the intrinsic geometry of the boundary, we transform the finite type points into strongly pseudoconvex ones. At these strongly pseudoconvex points we compute an explicit solution using the Henkin integral formula and we obtain estimates that we are able to pull back to the original domain. We achieve this by exploiting the branching behavior of the proper mapping. We also construct some biholomorphic numerical invariants associated with some of the domains under consideration.     

On the spectrum of the Cesàro operator C 1 on b\bar v_0 \cap \ell _\infty

In this paper we have investigated the spectrum of the Cesàro operator C ₁ which is regarded as an operator on the sequence space $b\bar v_0 \cap \ell _\infty $ the space of statistically null bounded variation sequences.     

On the rigidity of solitary waves for the focusing mass-critical NLS in dimensions d?2

For the focusing mass-critical NLS iut + △u =-|u| 4/d u,it is conjectured that the only global nonscattering solution with ground state mass must be a solitary wave up to symmetries of the equation.In this paper,we settle the conjecture for Hx1 initial data in dimensions d = 2,3 with spherical symmetry and d 4 with certain splitting-spherically symmetric initial data.     

Character formulas for Feigin–Stoyanovsky’s type subspaces of standard $\mathfrak{sl}(3, \mathbb{C})^{\widetilde{}}$-modules

Exact sequences of Feigin–Stoyanovsky’s type subspaces for affine Lie algebra \mathfraksl(l+1,\mathbbC)^[\tilde]\mathfrak{sl}(l+1,\mathbb{C})^{\widetilde{}} lead to systems of recurrence relations for formal characters of those subspaces. By solving the corresponding system for \mathfraksl(3,\mathbbC)^[\tilde]\mathfrak{sl}(3,\mathbb{C})^{\widetilde{}}, we obtain a new family of character formulas for all Feigin–Stoyanovsky’s type subspaces at the general level.     

Spectral Analysis for Stationary Solutions of the Cahn–Hilliard Equation in ℝ d

We consider the spectrum associated with three types of bounded stationary solutions for the Cahn–Hilliard equation on ? ^d , d ≥ 2: radial solutions, saddle solutions (only for d = 2), and planar periodic solutions. In particular, we establish spectral instability for each type of solution. The important case of multiply periodic solutions does not fit into the framework of our approach, and we do not consider it here.     

A finite-volume version of Aizenman–Higuchi theorem for the 2d Ising model

In the late 1970s, in two celebrated papers, Aizenman and Higuchi independently established that all infinite-volume Gibbs measures of the two-dimensional ferromagnetic nearest-neighbor Ising model at inverse temperature ${\beta\geq 0}$ are of the form ${\alpha\mu^{+}_\beta + (1-\alpha)\mu^{-}_\beta}$ , where ${\mu^{+}_\beta}$ and ${\mu^{-}_\beta}$ are the two pure phases and ${0\leq\alpha\leq 1}$ . We present here a new approach to this result, with a number of advantages: (a) We obtain an optimal finite-volume, quantitative analogue (implying the classical claim); (b) the scheme of our proof seems more natural and provides a better picture of the underlying phenomenon; (c) this new approach might be applicable to systems for which the classical method fails.     

Global solvability of the Cauchy problem for the Navier–Stokes equation in \mathbb {R}^3 for some class of initial data

In this paper we prove the existence of regular solutions to the Navier–Stokes equations if the initial data v ₀ have some finite weighted norm and supp v ₀ belongs to , is a ball with radius R ₀, where R ₀ is sufficiently large. The proof follows from appropriate estimates in weighted Sobolev spaces. K. Pileckas was supported by EC FP6 MC-ToK programme SPADE 2, MTKD-CT-2004-014508.     

Estimates of the levy constant for\sqrt p and class number one criterion for ℚ(\sqrt p )

Let p ≡ = 3 (mod 4) be a prime, let ?( $\sqrt p $ ) be the length of the period of the expansion of $\sqrt p $ into a continued fraction, and let h(4p) be the class number of the field ?( $\sqrt p $ ). Our main result is as follows. For p > 91, h(4p)=1 if and only if ?( $\sqrt p $ ) > 0.56 $\sqrt p $ L_4p(1), where L_4p(1) is the corresponding Dirichlet series. The proof is based on studying linear relations between convergents of the expansion of $\sqrt p $ into a continued fraction. Bibliography: 13 titles.     

Analogues of the central point theorem for families with d-intersection property in ℝ d

In this paper we consider families of compact convex sets in ? ^d such that any subfamily of size at most d has a nonempty intersection. We prove some analogues of the central point theorem and Tverberg’s theorem for such families.     

(Non-)Distributivity of the product for $$\sigma $$ σ -algebras with respect to the intersection

Archiv der Mathematik - We study the validity of the distributivity equation $$\begin{aligned} ({\mathcal {A}}\otimes {\mathcal {F}})\cap ({\mathcal {A}}\otimes {\mathcal {G}}) ={\mathcal...     

Gelfand–Kirillov Dimensions of the Z~2-graded Oscillator Representations of sl(n)

We find an exact formula of Gelfand–Kirillov dimensions for the infinite-dimensional explicit irreducible sl(n, F)-modules that appeared in the Z2-graded oscillator generalizations of the classical theorem on harmonic polynomials established by Luo and Xu. Three infinite subfamilies of these modules have the minimal Gelfand–Kirillov dimension. They contain weight modules with unbounded weight multiplicities and completely pointed modules.     

On the Construction of d—Continuous Modules

In this paper we introduce: and study the notion of dual Gontinuous (d-Contmuous) modnles, A decomposrtion thcorem for a d-continuous modules proved, this generahzes all known decompositron theorems for quasi-projective modules.     

Density lower bound estimates for local minimizers of the 2d Mumford–Shah energy

We prove, using direct variational arguments, an explicit energy-treshold criterion for regular points of 2-dimensional Mumford-Shah energy minimizers. From this we infer an explicit constant for the density lower bound of De Giorgi, Carriero and Leaci.     

Computation of the number representations of the elements of the ringℤ/dℤ as a sum of squares

The number of representations of the elements of the ringℤ/dℤ as a sum of invertible squares is computed, provided that each square occurs in the sum no more tha a fized number of times. For prime d an exhaustive answer is given in term of the class number and the fundamental unit of the real quadratic field . Biblography: 5 titles. Translted fromZapiski Nauchnykh Seminarov POMI, Vol. 227, 1995, pp. 5–8.     

On the Continuous Singularity of the Limit Distribution of Products of I.I.D. d×d Stochastic Matrices

This article gives sufficient conditions for the limit distribution of products of i.i.d. d×d random stochastic matrices, d finite and 2, to be continuous singular, when the support of the distribution of the individual random matrices is finite or countably infinite. Proofs are based on applications of the multivariate Central Limit Theorem.