On Exact Constant in the Generalized Poincare Inequality

Some problems concerning an exact constant in the generalized Poincare inequality with are discussed. In particular, the conjecture that the extremal of this problem is symmetric is confirmed. Bibliography: 7 titles.     

Protuberance effect in the generalized functional Strassen-Révész law

The set of increments of the Wiener process

A finiteness criterion for the number of rational points for twisted weil elliptic curves

We consider the Weil elliptic curve E/ℚ and let be its canonical L-series. Admitting the Birch-Swinnerton-Dyer conjecture and fixing the curve E, a criterion is given for the finiteness of the group E_D(ℚ) for twisted elliptic curves E_D, defined by the condition

On the numerical construction of an attractor for the Navier-Stokes system

In this paper the problem of the numerical approximation of the minimal global B-attractor for a semiflow generated by the Navier-Stokes equations in a two-dimensional bounded domain Ω is considered. The method suggested here is based on the formula , where G^N is a sequence of compact subsets of L₂(Ω), . The procedure of constructing G^N is finite and includes the numerical solution of the Navier-Stokes equations by means of the Galerkin method, together with an explicit finite-difference discretization in time. Bibliography: 5 titles. To dear teacher Olga A. Ladyzhenskaya on the occasion of the jubilee Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 200, 1992, pp. 91–97. Translated by V. I. Ochkur.     

Nikolskii type inequality for cardinal splines

The Nikolskii type inequality for cardinal splines

Parabolic twists for the linear algebras <Emphasis Type="Italic">A</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis>−1</Subscript>

New solutions of twist equations for the universal enveloping algebras U (A_n−1) are found. These solutions can be represented as products of full chains of extended Jordanian twists Abelian factors (“rotations”) , and sets of quasi-Jordanian twists . The latter are generalizations of Jordanian twists (with carrier b²) for special deformed extensions of the Hopf algebra U (b²). The carrier subalgebra for the composition is a nonminimal parabolic subalgebra in A _n−1 such that . The parabolic twisting elements are obtained in an explicit form. Details of the construction are illustrated by considering the examples n = 4 and n = 11. Bibliography: 21 titles. Published in Zapiski Nauchnykh Seminarov POMI, Vol. 347, 2007, pp. 187–213.     

SOME CONVERSE RESULTS ON ONESIDED APPROXIMATION ： JUSTIFICATIONS

The present paper deals with best onesided approximation rate in Lp spaces ^~En（f）Lp of f∈C2π.Although it is clear that the estimate ^~E(f)Lp≤C‖f‖Lp cannot be correct for all f∈L^p2π in case p＜∞, the question whether ~En(f)Lp≤Cω(f,n^-l)Lp or ^~En(f)Lp≤CEn(f)Lp holds for f∈ C2π remains totally untouched.Therefore it forms a basic problem to justify onesided approximation. The present paper will provide an answer to settle down the basis.     

The polya-1 property for convex approximation

If f∈L_p[0, 1], let f_p be its best L_p-approximant by convex functions. It is shown that if exists uniformly on closed subintervals of (0,1). This research was partially supported by Grant No. 020-033-58 from the Faculty Research Committee, Idaho State University.     

Some sharp estimates for the second continuity modulus for periodic functions and for functions extended from a segment

Let C be the space of 2π-periodic continuous real functions with the uniform norm, let H_n be the set of trigonometric polynomials of order not more than n, let ω₂(f) be the second continuity modulus for a function f∈C, and let T_n(f) be the best approximation polynomial of order n for f∈C. Set ; U:C→C; . In this paper, for h sufficiently large we find the values C(U,h) for some positive operators U. For example, C(A₀,h) and C(T₀,h) are found. For n=1,2,3 we find the values for some linear positive operators U:C→H_n. We establish relations between C(T₀,h) and exact constants in the inequality ω₂(f,h₁)≤C(h₁;h)ω₂(f,h) for some h and h₁ such that 0<h<h₁≤π. For a seminorm P invariant with respect to the shift and majorized by the uniform norm, analogs of C(U,h) are estimated from above. We investigate the problem of extension of a function defined on a segment with preservation of the second continuity modulus. The relation

Capacitary inequalities for fractional integrals,with applications to partial differential equations and Sobolev multipliers

Some new characterizations of the class of positive measures γ onR ⁿ such thatH _p ^l ∉L _p (γ) are given whereH _p ^l (1<p<∞ 0<l∞) is the space of Bessel potentials This imbed ding as well as the corresponding trace inequality

Equivariant D-modules attached to nilpotent orbits in a semisimple Lie algebra

Let _u be a compact Lie algebra and let _u be its complexification. Let ζ^−1/2 be the inverse on the set of regular elements of _u of a square root of the discriminant of . Generalizing a result of W. Lichtenstein in the case _u = (n, ℂ) or (nℝ), we prove that ∂(q).ζ^1/2 is non zero for all harmonic polynomialsq ∈S( ) \ {0}. This fact is deduced from results about equivariantD-modules supported on the nilpotent cone of .     

Convergence of weighted sums of independent random variables

Let {X_k} be a sequence of i.i.d. random variables with d.f. F(x). In the first part of the paper the weak convergence of the d.f.'s F_n(x) of sums is studied, where 0<α≤2, a_nk>0, 1≤k≤m_n, and, as n→∞, bothmax _1≤k≤mn_{a nk}→0 and . It is shown that such convergence, with suitably chosen A_n's and necessarily stable limit laws, holds for all such arrays {α_nk} provided it holds for the special case α_nk=1/n, 1≤k≤n. Necessary and sufficient conditions for such convergence are classical. Conditions are given for the convergence of the moments of the sequence {F_n(x)}, as well as for its convergence in mean. The second part of the paper deals with the almost sure convergence of sums , where a_n≠0, b_n>0, andmax _1≤k≤n a_k/b_n→0. The strong law is said to hold if there are constants A_n for which S_n→0 almost surely. Let N(0)=0 and N(x) equal the number of n≥1 for which b_n/|a_n|<x if x>0. The main result is as follows. If the strong law holds,EN (|X₁|)<∞. If for some 0<p≤2, then the strong law holds with if 1≤p≤2 and A_n=0 if 0<p<1. This extends the results of Heyde and of Jamison, Orey, and Pruitt. The strong law is shown to hold under various conditions imposed on F(x), the coefficients a_n and b_n, and the function N(x). Proceedings of the Seminar on Stability Problems for Stochastic Models, Moscow, 1993.     

Strict inequalities for the derivatives of functions satisfying certain boundary conditions

For functions satisfying the boundary conditions

Interior superconvergence error estimates for mixed finite element methods for second order elliptic problem

1.IntroductionLetfibeaplanedomainwithsmoothboundaryonandWm,p(fl)betheusualSobolevspaceonnwithnormWhenp=2,pisusuallyomitted.WeshalldenotetheusualinnerproductinL'(fl)orLa(O)'by','),andinL'(ofl)by't').Weshallusethesamenotationstoindicatethedualltiesbetw...     

On estimation and detection of a function of infinitely many variables

We observe an unknown function of infinitely many variables f = f(t), t = (t₁, ..., t_n, ... ) ∈, [0, 1]^∞, in the Gaussian white noise of level ε > 0. We suppose that in each variable there exists a 1-periodical σ-smooth extension of the function f(t) to IR ^∞. Taking a quantity σ > 0 and a positive sequence a = {a_k}, we consider the set that consists of functions f such that . We consider the cases a_k = k^α and a_k = exp(λk), α > 0, λ > 0. We would like to estimate a function f ∈ or to test the null hypothesis H₀: f = 0 against the alternatives f ∈ , where the set consists of functions f ∈ such that ∥f∥₂ ≥ r. In the estimation problem, we obtain the asymptotics (as ε → 0) of the minimax quadratic risk. In the detection problem, we study the sharp asymptotics of minimax separation rates f _ɛ ^* that provide distiguishability in the problems. Bibliography: 12 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 328, 2005, pp. 91–113.     

A trace formula for the scalar product of Hecke series and its applications

A trace formula expressing the mean values of the form (k=2,3,...)

A local duality theorem for categories of modules

Let Λ be an associative ring with identity and let be the category of left unitary Λ-modules. A subcateqory of the category is said to be small if the pairwise nonisomorphic objects of form a set. The main result of this paper consists of the fact that for every small full subcategory , there exists a ring Γ such that is dual to a small full subcategory of the category . Some applications of this result are indicated. Bibliography: 3 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 227, 1995, pp. 66–73.     

Carleson measures and the heat equation

Let { }, where { } is the open unit disk on the complex plane { }. In G, we consider analytic solutions u(t, z) ({ }, { }) of the heat equation 2u_t=u_zz with initial data f(z)=u(0, z) belonging to the Fock space F, i.e., to the space of entire functions square summable with the weight e−|z|2.Conditions on a nonnegative measure μ on G are described under which for all f ∈ F we have { } Bibliography: 17 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 247, 1997, pp. 146–155. Translated by S. V. Kislyakov.