Bijections on Rooted Trees with Fixed Size of Maximal Decreasing Subtrees

Recently, Seo and Shin showed that the number of rooted trees on [n + 1] = 1, 2, . . . , n+1 such that the maximal decreasing subtree with the same root has k + 1 vertices is equal to the number of functions f : [n] → [n] such that the image of f contains [k]. We give a bijective proof of this theorem.     

Product decompositions of the symmetric group induced by separable permutations

In this paper we consider the rank generating function of a separable permutation π in the weak Bruhat order on the two intervals [id,π] and [π,w₀], where w₀=n,n−1,…,1. We show a surprising result that the product of these two generating functions is the generating function for the symmetric group with the weak order. We then obtain explicit formulas for the rank generating functions on [id,π] and [π,w₀], leading to the rank-symmetry and unimodality of the two graded posets.     

A symmetric Roos bound for linear codes

The van Lint-Wilson AB-method yields a short proof of the Roos bound for the minimum distance of a cyclic code. We use the AB-method to obtain a different bound for the weights of a linear code. In contrast to the Roos bound, the role of the codes A and B in our bound is symmetric. We use the bound to prove the actual minimum distance for a class of dual BCH codes of length q²−1 over Fq. We give cyclic codes [63,38,16] and [65,40,16] over F₈ that are better than the known [63,38,15] and [65,40,15] codes.     

The Riemann-Hilbert approach to strong asymptotics for orthogonal polynomials on [−1,1]

We consider polynomials that are orthogonal on [−1,1] with respect to a modified Jacobi weight (1−x)^α(1+x)^βh(x), with α,β>−1 and h real analytic and strictly positive on [−1,1]. We obtain full asymptotic expansions for the monic and orthonormal polynomials outside the interval [−1,1], for the recurrence coefficients and for the leading coefficients of the orthonormal polynomials. We also deduce asymptotic behavior for the Hankel determinants and for the monic orthogonal polynomials on the interval [−1,1]. For the asymptotic analysis we use the steepest descent technique for Riemann-Hilbert problems developed by Deift and Zhou, and applied to orthogonal polynomials on the real line by Deift, Kriecherbauer, McLaughlin, Venakides, and Zhou. In the steepest descent method we will use the Szeg? function associated with the weight and for the local analysis around the endpoints ±1 we use Bessel functions of appropriate order, whereas Deift et al. use Airy functions.     

Ergodic transport theory and piecewise analytic subactions for analytic dynamics

We consider a piecewise analytic real expanding map f: [0, 1] ?? [0, 1] of degree d which preserves orientation, and a real analytic positive potential g: [0, 1] ?? ?. We assume the map and the potential have a complex analytic extension to a neighborhood of the interval in the complex plane. We also assume log g is well defined for this extension. It is known in Complex Dynamics that under the above hypothesis, for the given potential ?? log g, where ?? is a real constant, there exists a real analytic eigenfunction ? _?? defined on [0, 1] (with a complex analytic extension) for the Ruelle operator of ?? log g. Under some assumptions we show that $\frac{1} {\beta }\log \varphi _\beta$ converges and is a piecewise analytic calibrated subaction. Our theory can be applied when log g(x) = ?log f??(x). In that case we relate the involution kernel to the so called scaling function.     

Singular perturbations and vanishing passage through a turning point

The paper deals with planar slow-fast cycles containing a unique generic turning point. We address the question on how to study canard cycles when the slow dynamics can be singular at the turning point. We more precisely accept a generic saddle-node bifurcation to pass through the turning point. It reveals that in this case the slow divergence integral is no longer the good tool to use, but its derivative with respect to the layer variable still is. We provide general results as well as a number of applications. We show how to treat the open problems presented in Artés et al. (2009) [1] and Dumortier and Rousseau (2009) [13], dealing respectively with the graphics DI2a and DF1a from Dumortier et al. (1994) [14].     

Inverse spectral problems for Sturm-Liouville operators with singular potentials. Part III: Reconstruction by three spectra

We solve the inverse spectral problem of recovering the singular potential from W⁻¹₂(0,1) of a Sturm-Liouville operator by its spectra on the three intervals [0,1], [0,a], and [a,1] for some a∈(0,1). Necessary and sufficient conditions on the spectral data are derived, and uniqueness of the solution is analyzed.     

L 2-estimates with Levi-singular weight, and existence for\overline \partial

We give a symplectic proof of the link between pseudoconvexity of domains ofC ⁿ and of their boundaries (cf. [7, Th. 2.6.12]). Our approach also allows us to treat boundaries of codimension >1. We then extend the estimates by Hörmander in [7, Ch. 4, 5] and [6] toL ²-norms which haveC ¹ but notC ² weights and under a less restrictive assumption of weakq-pseudoconvexity. (A special trick is needed as a substitute for the method of thelowest positive eigenvalue of [6].)     

Hausdorff dimension of quasi-cirles of polygonal mappings and its applications

We show that the Hausdorff dimension of quasi-circles of polygonal mappings is one.Furthermore,we apply this result to the theory of extremal quasiconformal mappings.Let [μ] be a point in the universal Teichmller space such that the Hausdorff dimension of fμ(Δ) is bigger than one.We show that for every kn∈(0,1) and polygonal differentials ψn,n=1,2,...,the sequence {[kn ψn/|ψn|]} cannot converge to [μ] under the Teichmer metric.     

Pincement sur le spectre et le volume en courbure de Ricci positive

We shall show that a complete Riemannian manifold of dimension n with Ric?n−1 and its n-st eigenvalue close to n is both Gromov-Hausdorff close and diffeomorphic to the standard sphere. This extends, in an optimal way, a result of P. Petersen [Invent. Math. 138 (1999) 1] (as a by-product, we fill a gap stated in the erratum [Invent. Math. 155 (2004) 223]). We shall also show that a manifold with Ric?n−1 and volume close to is both Gromov-Hausdorff close and diffeomorphic to a space form Sn/π₁(M). This extends results of T. Colding [Invent. Math. 124 (1996) 175] and T. Yamaguchi [Math. Ann. 284 (1989) 423].     

Prescribing the Jacobian in critical spaces

We consider the Sobolev space $X = W^{s,p} \left( {\mathbb{S}^m ;\mathbb{S}^{k - 1} } \right)$ . We prove the existence of a robust distributional Jacobian Ju for u ∈ X, provided sp ≥ k ? 1; this generalizes a result of Bourgain, Brezis, and the second author [10] dealing with the case m = k. We identify the image of the map X ? u ? Ju in the critical case sp = k ? 1. This extends a result of Alberti, Baldo, and Orlandi [2] for s = 1 and p = k ? 1. We also present a new, analytical, dipole construction method.     

Dirac Operator with a Potential of Special Form and with the Periodic Boundary Conditions

We consider the Dirac operator on the interval [0, 1] with the periodic boundary conditions and with a continuous potential Q(x) whose diagonal is zero and which satisfies the condition Q(x) = Q^T(1?x), x ∈ [0, 1]. We establish a relationship between the spectrum of this operator and the spectra of related functional-differential operators with involution. We prove that the system of eigenfunctions of this Dirac operator has the Riesz basis property in the space L ₂ ² [0, 1].     

Un modèle du calcul de Dirac dans la théorie relative des ensembles

The aim of this Note is a new justification of the pertinence of the Dirac calculus (see [1]). We give a model of it in a relatively consistent set theory,the Relative Set Theory (see [2]). We have obtained this result by introducing a derivation of step functions.     

Symmetry in Generalized Quadrangles

In this paper, we describe some aspects of a Lenz(-Barlotti)-type classification of finite generalized quadrangles, which is being prepared by the author. Some new points of view are given. We also prove that each span-symmetric generalized quadrangle of order s > 1 with s even is isomorphic to $ \mathcal{Q} $ (4, s), without using the canonical connection (obtained by S. E. Payne in [15] between groups of order s ³ ? s with a 4-gonal basis and span-symmetric generalized quadrangle of order s. (The latter result was obtained for general s independently by W. M. Kantor in [10], and the author in [30] Finally, we obtain a classification program for all finite translation generalized quadrangles, which is suggested by the main results of [27], [30], [32], [35], [38] and [37].     

Discrepancy of Arithmetic Progressions in Higher Dimensions

K. F. Roth (1964, Acta. Arith.9, 257-260) proved that the discrepancy of arithmetic progressions contained in [1, N]={1, 2, …, N} is at least cN^1/4, and later it was proved that this result is sharp. We consider the d-dimensional version of this problem. We give a lower estimate for the discrepancy of arithmetic progressions on [1, N]^d and prove that this result is nearly sharp. We use our results to give an upper estimate for the discrepancy of lines on an N×N lattice, and we also give an estimate for the discrepancy of a related random hypergraph.     

On Orbits of Functions of the Volterra Operator

We study asymptotic properties of certain functions of the Volterra integral operator V in L ^p [0, 1] (1 ≤ p ≤ ∞). We also prove the Ritt property under minimal spectral assumptions for some functions of V in L ²[0, 1].     

The semiring of continous [0, 1]-valued functions

In this paper, we study the properties of prime ideals in semirings of continuous functions with values in the unit interval [0, 1] on topological spaces. We describe maximal and pure ideals of such semirings. We study homomorphisms of semirings of continuous [0, 1]-valued functions. In terms of semirings of functions we characterize some properties of compacta. We show that the theory of ideals in these semirings differs from the case of rings of continuous functions.     

Circuits through specified edges

We prove a theorem implying the conjecture of Woodall [14] that, given any k independent edges in a (k+1)-connected graph, there is a circuit containing all of them. This implies the truth of a conjecture of Berge [1, p.214] and provides strong evidence to a conjecture of Lovász [8].