An inverse problem of the three-dimensional wave equation for a general annular vibrating membrane with piecewise smooth boundary conditions

This paper deals with the very interesting problem about the influence of piecewise smooth boundary conditions on the distribution of the eigenvalues of the negative Laplacian inR ³. The asymptotic expansion of the trace of the wave operator $\widehat\mu (t) = \sum\limits_{\upsilon = 1}^\infty {\exp \left( { - it\mu _\upsilon ^{1/2} } \right)} $ for small ?t? and $i = \sqrt { - 1} $ , where $\{ \mu _\nu \} _{\nu = 1}^\infty $ are the eigenvalues of the negative Laplacian $ - \nabla ^2 = - \sum\limits_{k = 1}^3 {\left( {\frac{\partial }{{\partial x^k }}} \right)} ^2 $ in the (x ¹,x ²,x ³), is studied for an annular vibrating membrane Ω inR ³ together with its smooth inner boundary surfaceS ₁ and its smooth outer boundary surfaceS ₂. In the present paper, a finite number of Dirichlet, Neumann and Robin boundary conditions on the piecewise smooth componentsS ^* _i(i=1, …,m) ofS ₁ and on the piecewise smooth componentsS ^* _i(i=m+1, …,n) ofS ₂ such that $S_1 = \bigcup\limits_{i = 1}^m {S_i^* } $ and $S_2 = \bigcup\limits_{i = m + 1}^n {S_i^* } $ are considered. The basic problem is to extract information on the geometry of the annular vibrating membrane ω from complete knowledge of its eigenvalues by analyzing the asymptotic expansions of the spectral function $\widehat\mu (t)$ for small ?t?.     

Finite-dimensionality of bounded invariant sets for Navier-stokes systems and other dissipative systems

One proves the finite-dimensionality of a bounded set M of a Hilbert space H, negatively invariant relative to a transformation V, possessing the following properties: For any points υ and \(\tilde \upsilon\) of the set M one has $$\left\| {V(\upsilon ) - V(\tilde \upsilon )} \right\| \leqslant \ell \left\| {\upsilon - \tilde \upsilon } \right\|$$ , while $$\left\| {Q_n V(\upsilon ) - Q_n V(\tilde \upsilon )} \right\| \leqslant \delta \left\| {\upsilon - \tilde \upsilon } \right\|, \delta< 1$$ ,δ<1 where Q_n is the orthoprojection onto a subspace of codimension n. With the aid of this result and of the results found in O. A. Ladyzhenskaya's paper “On the dynamical system generated by the Navier-stokes equations” (J. Sov. Math.,3, No. 4 (1975)) one establishes the finite-dimensionality of the complete attractor for two-dimensional Navier-Stokes equations. The same holds for many other dissipative problems.     

On the number of non-isomorphic subgraphs

Let $\mathcal{K}$ be the family of graphs on ω₁ without cliques or independent subsets of sizew ₁. We prove that

1. it is consistent with CH that everyGε $\mathcal{K}$ has 2^ω many pairwise non-isomorphic subgraphs,
2. the following proposition holds in L: (*)there is a Gε $\mathcal{K}$ such that for each partition (A, B) of ω₁ either G?G[A] orG?G[B],
3. the failure of (*) is consistent with ZFC.

     

Approximation to the transcendental relationship of two algebraic points of the function\wp \left( z \right) with complex multiplication

For fixed ?>0, the following inequality holds: $$\left| {\frac{u}{\upsilon } - \wp } \right| > Cexp\left( { - \left( {lnH} \right)^{2 + \varepsilon } } \right)$$ for all numbers β belonging to a field K of finite degree over Q. The constant C>0 does not depend on β. H is the height of β. \(\wp \) (u) and \(\wp \) (v) are algebraic numbers, and u/v is a transcendental number. \(\wp \) (z) is the Weierstrass function with complex multiplication and algebraic invariants. The proof is ineffective.     

L 1 decay properties for a semilinear parabolic system

This article is concerned with the decay property in theL ¹ norm ast»∞ of the nonnegative solutions of the initial value problem in ? ⁿ $\left\{ {\begin{array}{*{20}c} {u_t = \Delta u + \mu |\nabla \upsilon |^q } \\ {\upsilon _t = \Delta \upsilon + \upsilon |\nabla \upsilon |^p } \\ \end{array} } \right.$ for different values of the parametersp, q≥1 and when μ, ν<0. If $pq > \frac{{\inf \left( {p,q} \right)}}{{n + 1}} + \left( {n + 2} \right)/\left( {n + 1} \right)$ then lim _t→∞∥u(t)+v(t)∥₁>0 and when $pq< \frac{{\inf \left( {p,q} \right)}}{{n + 1}} + \left( {n + 2} \right)/\left( {n + 1} \right)$ then lim _t→∞∥u(t)+v(t)∥₁>0.     

Geométrie des suites de Kronecker

Let Θ be a element of the d-dimensional torus $\mathbb{T}$ ^d andτ the translationτ(x)=x + Θ. When d=1 there existe some partitions of $\mathbb{T}$ ¹ which are associated withτ. We prove the existence of partitions of $\mathbb{T}$ ^d which enjoyed the same kind of properties and whose elements (A _i ) _i≤n are convex polytopes. We also give a lower bound for the isotropic discrepancy of the sequence (nΘ) _nε?.     

Cosymplectic quasi-Sasakian pseudo-Riemannian manifolds and coisotropic foliations

Si considera una varietà neutra \(\tilde M\) di dimensione 2m munita di una struttura conforme simplettica \(CS_p \left( {2m; R} \right) = \left( {\tilde \Omega , \tilde \upsilon } \right)\) . Vengono studiati i differenti problemi concernenti gli automorfismi infinitesimali della 2-forma quasi simplettica \(\tilde \Omega \) . Inoltre vengono formulate alcune proprietà di un fogliettamento con isotropoF _c su \(\tilde M\) .     

A multivariate analog of Marsden's identity and a quasi-interpolation scheme

Let ? be a linear combination of certain box splines and \(\hat \phi \) its Fourier transform, such that \(\hat \phi \left( 0 \right) \ne 0\) and \(D^\beta \hat \phi \left( {2\pi k} \right) = 0\) for all κ∈Z^N{0} and β≤α. In this paper we construct an expression of the multivariate polynomial (·-y)^α in terms of a linear combination of the integer translates of ?(·), where the coefficients can be computed recursively using only the information on \(D^\beta \hat \phi \left( 0 \right)\) , β ≤ α. As an application, a quasi-interpolation scheme based only on function values on (scaled) integers κ∈Z^N is constructed that gives a “multivariate order” of approximation that includes both coordinate and total orders.     

\mathfrak{E} of topological spaces II

In this paper, we obtain analogues, in the situation of \(\mathfrak{E}\) -extensions, of Magill's theorem on lattices of compactifications. We define an epireflective subcategory of the categoryT 2 of all Hausdorff spaces to be admissive (respectively finitely admissive) if for any \(\mathfrak{E}\) -regular spaceX, every Hausdorff quotient of \(\beta _\mathfrak{E} X\) which is Urysohn on \(\beta _\mathfrak{E} X - X\) (respectively which is finitary on \(\beta _\mathfrak{E} X - X\) ) and which is identity onX, has \(\mathfrak{E}\) . We notice that there are many proper epireflective subcategories ofT 2 containing all compact spaces and which are admissive; there are many such which are not admissive but finitely admissive. We prove that when \(\mathfrak{E}\) is a finitely admissive epireflective subcategory ofT 2, then the lattices of finitary \(\mathfrak{E}\) -extensions of two spacesX andY are isomorphic if and only if \(\beta _\mathfrak{E} X - X\) and \(\beta _\mathfrak{E} Y - Y\) are homeomorphic. Further if \(\mathfrak{E}\) is admissive, then the lattices of Urysohn \(\mathfrak{E}\) -extensions ofX andY are isomorphic if and only if \(\beta _\mathfrak{E} X - X\) and \(\beta _\mathfrak{E} Y - Y\) are homeomorphic.     

On positive definite measures

In this paper we study the Fourier transform of unbounded measures on a locally compact groupG. After a short introductory section containing background material, especially results established byL. Argabright andJ. Gil De Lamadrid we turn to the main subjects of the paper: first we characterize \(\Re \left( G \right), \mathfrak{J}\left( G \right)\) andB(G) cones in \(\mathfrak{W}\left( G \right)\) . After that we establish the subspace \(\mathfrak{W}_\Delta \left( G \right)\) of \(\mathfrak{W}\left( G \right)\) which contains \(\mathfrak{W}_p \left( G \right)\) , the linear span of all positive definite measures.     

The chromatic polynomial between graph & its complement—about Akiyama and Hararys' open problem

In 1980, Akiyama and Harary proposed the following problem in the Proceedings-Fourth International Graph Theory Conference: “Are there any graphsG which are not self-complementary withG and $\bar G$ having the same chromatic polynomial?”. The problem has been unsolved until now. This paper proves that there are no graphsG which are not self-complementary withG and $\bar G$ having the same chromatic polynomial when |V(G)| =p < 8 orp = 2, 3 (mod 4), there must be a graphG which are not self-complementary withG and $\bar G$ having the same chromatic polynomial when |V(G)| =p ≥ 8 andp ≡ 0, 1 (mod 4).     

Between\widehat{gl}(\infty ) and\widehat{sl}_N affine algebras. I. Geometrical actions

We consider the central extended $\widehat{gl}(\infty )$ Lie algebra and a set of its subalgebras parametrized by |q|=1, which coincides with the embedding of the quantum tori Lie algebras (QTLA) in $\widehat{gl}(\infty )$ . Forq ^N=1 there exists an ideal, and a factor over this ideal is isomorphic to an $\widehat{sl}_{N(z)} $ affine algebra. For a generic valueq the corresponding subalgebras are dense in $\widehat{gl}(\infty )$ . Thus, they interpolate between $\widehat{gl}(\infty )$ and $\widehat{sl}_{N(z)} $ . All these subalgebras are fixed points of automorphism of $\widehat{gl}(\infty )$ . Using the automorphisms, we construct geometrical actions for the subalgebras, starting from the Kirillov-Kostant form and the corresponding geometrical action for $\widehat{gl}(\infty )$ .     

A ℤ-Simplex Algorithm with partial updates

The Simplex primal and dual methods, for the solution of $$\max \left\{ {c^T x:Ax = b, x \geqslant 0} \right\},$$ were presented previously in terms of certain bases ? and \(\mathbb{Y}\) ofN(A) andR(A ^T ) respectively. In these implementations, called the ?-Simplex Algorithm and the \(\mathbb{Y}\) -Dual Method, the bases ? and \(\mathbb{Y}\) (giving the edges of the polyhedron in question at the given basic feasible solution) are updated at each iteration. In this paper we show that only partial updates of ? are needed in the ?-Simplex Algorithm, analogously to the partial updates in the Revised Simplex Algorithm. Similar results can be given for the \(\mathbb{Y}\) -Dual Method.     

Exactn-widths of hardy-sobolev classes

Let $\tilde h^r _{\infty ,\beta } $ and $\tilde H^r _{\infty ,\beta } $ denote those 2π-periodic, real-valued functions onR that are analytic in the strip |Imz|<β and satisfy the restrictions |Ref ^(r)(z)| ≤ 1 and |f ^(r)(z)| ≤ 1, respectively. We determine the Kolmogorov, linear, and Gel’fand widths of $\tilde h^r _{\infty ,\beta } $ inL _q[0, 2π], 1 ≤q ≤ ∞, and $\tilde H^r _{\infty ,\beta } $ inL _∞[0, 2π].     

Об операторе Кальдерона

The Calderon type operator $$Sx(t) = \int\limits_0^\infty {x(s)d\mathop {\min }\limits_{i = 0,1} \{ \varphi _i (s)/\Psi _\iota (t)\} } $$ is investigated from the point of view of its bounded action in symmetric spaces of measurable functions on [0, ∞), whereφ _i(t) andΨ _i(t) are concave positive functions on [0, ∞). The following assertions are proved. Theorem 1. Let 1) \(\alpha _{\varphi _1 } > \beta (E) \geqq \alpha (E) > \beta _{\varphi _0 } ,\) , 2)either \(\beta _{\psi _0 }< 1\) or \(\beta _{\psi 1}< 1\) ,where \(\alpha _{\varphi _1 } \) and \(\beta _{\psi _1 } \) denote exponents of the functions φ _i and Ψ_i, i=0, 1,and α(E),β(E) are indices of the space E. Then the Calderon operator acts boundedly from E into E _δ,where δ(t) and χ(t) stand for measurable solutions of the equations $$\psi _i (\delta (t)) = \chi (t)\varphi _i (t),i = 0,1,$$ and $$||x||_{E_{\delta ,\chi } } = ||x^{**} (\delta (t))\chi (t)||_E .$$ Theorem 2.If the ratio φ ₀/φ(t)/φ₁(t) is non-increasing, Ψ_i(t) are semimultiplicative and \(\alpha _{\psi _i } \) (i=0, 1),then a necessary condition for the Calderon operator to act boundedly from E into E _{δ, χ} $$\beta _{\varphi _1 } \geqq \beta (E) \geqq \alpha (E) \geqq \alpha _{\varphi _0 } .$$      

L 2 existence theorems for the\bar \partial _b - Neumann problem on strongly pseudoconvex CR manifoldsproblem on strongly pseudoconvex CR manifolds

LetM be the boundary of a strongly pseudoconvex domain in \(\mathbb{C}^n \) ,n≥4 and ω be an open subset inM such that ?ω is the intersection ofM with a flat hypersurface. We establish theL ² existence theorems of the \(\bar \partial _b - Neumann\) problem on ω. In particular, we prove that the \(\bar \partial _b - Laplacian\) \(\square _b = \bar \partial _b \bar \partial _b^* + \bar \partial _b^* \bar \partial _b \) equipped with a pair of natural boundary conditions, the so-called \(\bar \partial _b - Neumann\) boundary conditions, has closed range when it acts on (0,q) forms, 1≤q≤n?3. Thus there exists a bounded inverse operator for \(\square _b \) , the \(\bar \partial _b - Neumann\) operatorN _b, and we have the following Hodge decomposition theorem on ω for \(\bar \partial _b \bar \partial _b^* N_b \alpha + \bar \partial _b^* \bar \partial _b N_b \alpha \) , for any (0,q) form α withL ²(ω) coefficients. The proof depends on theL ^p regularity of the tangential Cauchy-Riemann operators \(\bar \partial _b u = \alpha \) on ω?M under the compatibility condition \(\bar \partial _b \alpha = 0\) , where α is a (p, q) form on ω, where 1≤q≤n?2. The interior regularity ofN _b follows from the fact that \(\square _b \) is subelliptic in the interior of ω. The operatorN _b induces natural questions on the regularity up to the boundary ?ω. Near the characteristic point of the boundary, certain compatibility conditions will be present. In fact, one can show thatN _b is not a compact operator onL ²(ω).     

The number of non-isomorphic models in quasi-varieties of semigroups

Define \( n_K (\lambda )\) tobe eitherω, or the number of non-isomorphic algebras in \(K\) ] having cardinality λ, whichever cardinal is larger. It is proved here that if \(K\) ] is a quasi-variety (universal Horn class) of semigroups, then \(n_K\) is one of four functions. Each of these functions satisfies: \(n_K (\omega ) = \omega\) or \(n_K (\omega ) = 2^\omega\) . If \(n_K (\lambda )< 2^\lambda\) for some infinite λ then \(K\) ] is a residually finitevariety.     

A note on periodic solutions of a differential equation with two parameters

In [1] (p. 215), the authors Andronov, Leontovich-Andronova, Gordon, and Maier, consider the following equation: $$\left\{ \begin{gathered} \tfrac{{dx}}{{dt}} = y, \hfill \\ \tfrac{{dy}}{{dt}} = x + x^2 - \left( {\varepsilon _1 + \varepsilon _2 x} \right)y, \hfill \\ \end{gathered} \right.$$ whereε ₁ andε ₂ are real constants andε ₁ andε ₂ are not both zero. They proved that there are no non-trivial periodic solutions except possibly for the case $0< \tfrac{{\varepsilon _1 }}{{\varepsilon _2 }}< \tfrac{3}{2}$ . They left that case as an open problem. In this note we prove that there are indeed no non-trivial periodic solutions in the case $0< \tfrac{{\varepsilon _1 }}{{\varepsilon _2 }}< \tfrac{3}{2}$ either. Our method of proof consists essentially of constructing a Dulac function (see [6] and [9]) and using the conception of Duff's rotated vector field (see [4], [7], [8], [10], and [11]).     

Analytische Fortsetzbarkeit von zufälligen Potenzreihen bezüglich abhängiger Zufallsvariabler

Рассматриваются слу чайная величина \(\mathfrak{X} = (X_n (\omega ))\) , удовлетворяющая усл овиюE(X _n ⁴ )≦M, и соответствующ ий случайный степенн ой ряд \(f_x (z;\omega ) = \mathop \sum \limits_{n = 0}^\infty a_n X_n (\omega )z^n\) . Устанавливаются тео ремы непродолжимост и почти наверное:

1. дляf _x при условиях с лабой мультипликати вности на \(\mathfrak{X}\) ,
2. для \(f_{\tilde x}\) , где \(\mathop \mathfrak{X}\limits^ \sim = (\mathop X\limits^ \sim _n )\) есть подп оследовательность в \(\mathfrak{X}\) ,
3. для по крайней мере од ного из рядовf _x′ илиf _x″ , где \(\mathfrak{X}'\) и \(\mathfrak{X}''\) — некоторые п ерестановки \(\mathfrak{X}\) , выбираемые универс ально, т. е. независимо от коэффициентовa _n .

     

New estimates of continuity in $$M/GI/1/ \infty$$ queues

The paper deals with an estimation of the total variation distance between stationary distributions of waiting time in two queueing systems with equal Poisson inputs and different distributions B and $\widetilde B$ of service time. Assuming equality of two first moments of B and $\widetilde B$ the continuity inequalities are derived in terms of difference pseudomoments of B and $\widetilde B$ . When in addition the third moments of B and $\widetilde B$ coincide then the constant involved in the corresponding inequality has the asymptotics ${\text{O}}\left[ {\left( {1 - \rho } \right)^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} } \right]$ in the heavy traffic limit $\rho \to 1$ .