Regular quantizations and covering maps

Let $\tilde{M} \rightarrow MLet be a holomorphic (unbranched) covering map between two compact complex manifolds, with . We prove that if and M both admit regular K?hler forms and ω respectively then, up to homotheties, and (M, ω) are biholomorphically isometric. This work was supported by the M.I.U.R. Project “Geometric Properties of Real and Complex Manifolds”.     

Normality of Products of <Emphasis Type="Italic">p</Emphasis>-Hyponormal Operators and Their Aluthge Transforms

Let B(H) denote the algebra of operators on a complex separable Hilbert space H, and let A $\in$ B(H) have the polar decomposition A = U|A|. The Aluthge transform is defined to be the operator . We say that A $\in$ B(H) is p-hyponormal, . Let . Given p-hyponormal , such that AB is compact, this note considers the relationship between denotes an enumeration in decreasing order repeated according to multiplicity of the eigenvalues of the compact operator T (respectively, singular values of the compact operator T). It is proved that is bounded above by and below by for all j = 1, 2, . . . and that if also is normal, then there exists a unitary U¹ such that for all j = 1, 2, . . ..     

Piecewise projective homeomorphisms and a noncommutative Steinberg extension

Let CP (R) be the group of compactly supported homeomorphisms ofR= which are piecewise with a parabolic defect at each breakpoint. An acyclic extension

On the Range of the Aluthge Transform

Let be the algebra of all bounded linear operators on a complex separable Hilbert space For an operator let be the Aluthge transform of T and we define for all where T = U|T| is a polar decomposition of T. In this short note, we consider an elementary property of the range of Δ. We prove that R(Δ) is neither closed nor dense in However R(Δ) is strongly dense if is infinite dimensional. An erratum to this article is available at .     

Quasi-uniform completions of partially ordered spaces

In this paper we define partially ordered quasi-uniform spaces (X, , ≤) (PO-quasi-uniform spaces) as those space with a biconvex quasi-uniformity on the poset (X, ≤) and give a construction of a (transitive) biconvex compatible quasi-uniformity on a partially ordered topological space when its topology satisfies certain natural conditions. We also show that under certain conditions on the topology of a PO-quasi-uniform space (X, , ≤), the bicompletion of (X, ) is also a PO-quasi-uniform space ( , ⪯) with a partial order ⪯ on that extends ≤ in a natural way.      

Perturbation Bounds for the Polar Factors

Let $A$, $\tilde{A}\in C^{m\times n}$, rank (A)=rank ($\tilde{A}$)=$n$. Suppose that $A=QH$ and $\tilde{A}=\tilde{Q}\tilde{H}$ are the polar decompositions of $A$ and $\tilde{A}$, respectively. It is proved that $$\|\tilde{Q}-Q\|_F\leq 2\|A^+\|_2\|\tilde{A}-A\|_F$$ and $$\|\tilde{H}-H\|_F\leq \sqrt{2}\|\tilde{A}-A\|_F$$ hold, where $A^+$ is the Moore-Penrose inverse of $A$, and $\| \|_2$ and $\| \|_F$ denote the spectral norm and the Frobenius norm, respectively.     

Perturbazioni per processi di controllo con parametri distribuiti

We consider the control processes $$\begin{gathered} (E) z_{xy} + A(x,y)z_x + B(x,y)z_y + C(x,y)z = F(x,y)U(x,y) \hfill \\ q.o. in R = [0,\alpha [ \times [0,\beta [, \hfill \\ \end{gathered} $$ $$\begin{gathered} (\tilde E) z_{xy} + \bar A(x,y)z_x + \bar B(x,y)z_y + \bar C(x,y)z = \bar F(x,y)U(x,y) \hfill \\ q.o. in R \hfill \\ \end{gathered} $$ We show that under appropriate assumptions on the dataA, B, C, F, if the process (E) is completely controllable, then the perturbed process (ē) is completely controllable too. The result is obteined proving for the evolution matrixV, a continuous dependence on the coefficientsA, B, C.     

$$\tilde{A}$$ and $$\tilde{D}$$ type cluster algebras: triangulated surfaces and friezes

Journal of Algebraic Combinatorics - By viewing $$\tilde{A}$$ and $$\tilde{D}$$ type cluster algebras as triangulated surfaces, we find all cluster variables in terms of either (i) the frieze...     

A Higher-Order Analog of the Linking Number for a Pair of Divergence-Free Vector Fields

Pairs B, of divergence-free vector fields with compact support in are considered higher-order analog M(B, c (of order 3) of the Gauss helicity number H(B, )= , curl(A)=B; (of order 1) is constructed, which is invariant under volume-preserving diffeomorphisms. An integral expression for M is given. A degree-four polynomial m(B(x₁), B(x₂), ( ₁), ( ₂)), x₁, x₂, _{1 2} , is defined, which is symmetric in the first and second pairs of variables separately. M is the average value of m over arbitrary configurations of points. Several conjectures clarifying the geometric meaning of the invariant and relating it to invariants of knots and links are stated. Bibliography: 11 titles.     

A Comparison on the Commutative Neutrix Convolution of Distributions and the Exchange Formula

Let , be ultradistributions in and let and where is a sequence in which converges to the Dirac-delta function . Then the neutrix product is defined on the space of ultradistributions as the neutrix limit of the sequence provided the limit exist in the sense that

A spinorial analogue of Aubin’s inequality

Let (M, g, σ) be a compact Riemannian spin manifold of dimension ≥ 2. For any metric conformal to g, we denote by the first positive eigenvalue of the Dirac operator on . We show that

Lefschetz decompositions and categorical resolutions of singularities

Let Y be a singular algebraic variety and let be a resolution of singularities of Y. Assume that the exceptional locus of over Y is an irreducible divisor in . For every Lefschetz decomposition of the bounded derived category of coherent sheaves on we construct a triangulated subcategory ) which gives a desingularization of . If the Lefschetz decomposition is generated by a vector bundle tilting over Y then is a noncommutative resolution, and if the Lefschetz decomposition is rectangular, then is a crepant resolution.     

The Cosserat eigenfunctions for the elliptic exterior problem with applications to thermoelasticity and Stokes flow

The Cosserat eigenvalue problem for the elliptic exterior is considered. It is shown that the only Cosserat eigenvalue different from the infinite multiple eigenvalues and is which also has an infinite multiplicity. The orthogonal basis of the eigenspace corresponding to is constructed. Application to thermoelasticity and Stokes flow – extensional and shear – past a rigid elliptical cylinder are presented and agreement is obtained with classical solutions for a circle. The fact that the solutions consist of only two eigenfunctions reveals the efficiency of the method.Received: February 27, 2003     

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.     

Third Derivative of the One-Electron Density at the Nucleus

We study electron densities of eigenfunctions of atomic Schr?dinger operators. We prove the existence of , the third derivative of the spherically averaged atomic density at the nucleus. For eigenfunctions with corresponding eigenvalue below the essential spectrum in any symmetry subspace we obtain the bound , where Z denotes the nuclear charge. This bound is optimal. ? 2008 by the authors. This article may be reproduced in its entirety for non-commercial purposes. Submitted: April 22, 2008. Accepted: July 7, 2008.     

The Perturbation Analysis of the Product of Singular Vector Matrices $UV^T$

Let A be an $n\times n$ nonsingular real matrix, which has singular value decomposition $A=U\sum V^T$. Assume A is perturbed to $\tilde{A}$ and $\tilde{A}$ has singular value decomposition $\tilde{A}=\tilde{U}\tilde{\sum}\tilde{V}^T$. It is proved that $\|\tilde{U}\tilde{V}^T-UV^T\|_F\leq \frac{2}{\sigma_n}\|\tilde{A}-A\|_F$, where $\sigma_n$ is the minimum singular value of A; $\|\dot\|_F$ denotes the Frobenius norm and $n$ is the dimension of A. This inequality is applicable to the computational error estimation of orthogonalization of a matrix, especially in the strapdown inertial navigation system.     

On the irreducibility of the Severi variety of nodal curves in a smooth surface

Archiv der Mathematik - Let X be a smooth projective surface and $$L\in \mathrm {Pic}(X)$$ . We prove that if L is $$(2k-1)$$ -spanned, then the set $${\tilde{V}}_k(L)$$ of all nodal and...     

Birth delay of a Markov process and the stopping distributions for regular processes

Summary We consider Markov processes with a fixed transition functionp(r, x; t, B) and with random birth times. We show that a process can be obtained from (X _t ,P) by birth delay if and only if for allt andB. As an application, we give a new version and a new proof of the results of Rost [R] and Fitzsimmons [F2] on stopping distributions of Markov processes. The key Lemma 1.1 replaces the filling scheme used by the previous authors.Birth delay was considered from a different prospective in [F1].Partially supported by the National Science Foundation Grant DMS-8802667     

A note on the divergence of geodesic rays in manifolds without conjugate points

Let (M, g) be a compact Riemannian manifold without conjugate points and let be its universal covering endowed with the pullback of the metric g by the covering map. We show that geodesic rays in which meet an axis of a covering isometry diverge from this axis. This result generalizes well known results by Morse and Hedlund in the context of globally minimizing geodesics in the universal covering of compact surfaces.      

Bemerkungen zur Deformationstheorie nichtrationaler Singularitäten

Let be a 1-convex holomorphic mapping between complex spaces resp.S, and let be the blowingdown factorization of over S. We prove in part 1 of the present note: The fiber ^–1(s₀) over a point s₀S is the Remmert quotient of if and only if every holomorphic function on (defined in a neighborhood of the exceptional subvariety of that fiber) can be extended holomorphically to . This is true, for instance, in the case: flat, S reduced at s₀ and dim , =const for all sS. In part 2, we use this result to obtain the following: For any Riemann surface R with genus g2 there exists a 2-dimensional normal complex analytic singularity X such that the minimal resolution of X contains R as exceptional subvariety, and has a deformation over the unit disc S={|s|<1} which can not be blown down to a deformation of X.