Generic properties of invariant measures for continuous piecewise monotonic transformations

We endow the set of all invariant measures of topologically transitive subsetsL withh _top (L)>0 of a continuous piecewise monotonic transformation on [0, 1] with the weak topology. We show that the set of periodic orbit measures is dense, that the sets of ergodic, of nonatomic, and of measures with supportL are denseG -sets, that the set of strongly mixing measures is of first category, and that the set of measures with zero entropy contains a denseG -set.     

Doubling measures on Cantor sets and their extensions

We study the doubling property of binomial measures on the middle interval Cantor set. We obtain a necessary and sufficient condition that enables a binomial measure to be doubling. Then we determine those doubling binomial measures which can be extended to be doubling on [0,1]. Finally, we construct a compact set X in [0,1] and a doubling measure μ on X, such that [`(F)]_X=X\overline{F}_{X}=X and m|_EX{\mu|}_{E_{X}} is doubling on E _X , where E _X is the set of accumulation points of X and F _X is the set of isolated points of X.     

Nonnegatively curved fixed point homogeneous manifolds in low dimensions

Let G be a compact Lie group acting isometrically on a compact Riemannian manifold M with nonempty fixed point set M ^G . We say that M is fixed-point homogeneous if G acts transitively on a normal sphere to some component of M ^G . Fixed-point homogeneous manifolds with positive sectional curvature have been completely classified. We classify nonnegatively curved fixed-point homogeneous Riemannian manifolds in dimensions 3 and 4 and determine which nonnegatively curved simply-connected 4-manifolds admit a smooth fixed-point homogeneous circle action with a given orbit space structure.     

Metric,Fractal Dimensional and Baire Results on the Distribution of Subsequences

Let X be a locally compact metric space. One important object connected with the distribution behavior of an arbitrary sequence x on X is the set M( x ) of limit measures of x . It is defined as the set of accumulation points of the sequence of the discrete measures induced by x . Using binary representation of reals one gets a natural bijective correspondence between infinite subsets of the set ℕ of positive integers and numbers in the unit interval I = 〈0, 1]. Hence to each sequence x = (x_n)_n∈ℕ ∈ X^ℕ and every a I there corresponds a subsequence denoted by a x . We investigate the set M(a x ) for given x with emphasis on the behavior for “typical” a in the sense of Baire category, Lebesgue measure and Hausdorff dimension.     

On intrinsic ergodicity of piecewise monotonic transformations with positive entropy

We consider a class of piecewise monotonically increasing functionsf on the unit intervalI. We want to determine the measures with maximal entropy for these transformations. In part I we construct a shift-space Σ _f ⁺ isomorphic to (I, f) generalizing the \-shift and another shift Σ _M over an infinite alphabet, which is of finite type given by an infinite transition matrixM. Σ _M has the same set of maximal measures as (I, f) and we are able to compute the maximal measures of maximal measures of. In part II we try to bring these results back to (I, f). There are only finitely many ergodic maximal measures for (I, f). The supports of two of them have at most finitely many points in common. If (I, f) is topologically transitive it has unique maximal measure.     

Measures of affinity of a sequence for a number

We define strong and weak affinities of a number a for a sequence (x_k ) denoted by L (a,(x_k )) and U (a, (x_k )) respectively. We show U (a,(x_k )) > 0 if and only if the number a is a statistical limit point of the sequence (x_k ). We consider the distribution of sequences with positive weak and strong measures of affinity within the space l ^∞ of bounded sequences. The main result is that the set of bounded sequences with U (a,(x_k )) > 0, that is, the set of sequences with statistical limit points, is a dense subset in l ^∞ of the first category. We also show the set of sequences with positive strong affinities is a nowhere dense subset of l ^∞.     

Description of weakly periodic Gibbs measures for the isingmodel on a cayley tree

We introduce the concept of a weakly periodic Gibbs measure. For the Ising model, we describe a set of such measures corresponding to normal subgroups of indices two and four in the group representation of a Cayley tree. In particular, we prove that for a Cayley tree of order four, there exist critical values T _c < T _cr of the temperature T > 0 such that there exist five weakly periodic Gibbs measures for 0 < T < T _c or T > T _cr , three weakly periodic Gibbs measures for T = T _c , and one weakly periodic Gibbs measure for T _c < T ≤ T _cr . __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 156, No. 2, pp. 292–302, August, 2008.     

The bar derived category of a curved dg algebra

Curved A_∞-algebras appear in nature as deformations of dg algebras. We develop the basic theory of curved A_∞-algebras and, in particular, curved dg algebras. We investigate their link with a suitable class of dg coalgebras via the bar construction and produce Quillen model structures on their module categories. We define the analogue of the relative derived category for a curved dg algebra.     

On surface area measures of convex bodies

The set L _j of jth-order surface area measures of convex bodies in d-space is well known for j=d–1. A characterization of L _j was obtained by Firey and Berg. The determination of L _j, for j{2, ..., d–2}, is an open problem. Here we show some properties of L _j concerning convexity, closeness, and size. Especially we prove that the difference set L _j–L _j is dense (in the weak topology) in the set of signed Borel measures on the unit sphere which have barycentre 0.     

Asymptotic properties of the algebraic moment range process

Let M _n denote the n-th moment space of the set of all probability measures on the interval [0, 1], P _n the uniform distribution on the set M _n and r _{n + 1} the maximal range of the (n + 1)-th moments corresponding to a random moment point C _n with distribution P _n on M _n . We study several asymptotic properties of the stochastic process (r _⌊nt⌋+1) _t∈[0,T] if n → ∞. In particular weak convergence to a Gaussian process and a large deviation principle are established.      

Simultaneous intersection representation of pairs of graphs

We characterize the pairs (G₁, G₂) of graphs on a shared vertex set that are intersection polysemic: those for which the vertices may be assigned subsets of a universal set such that G₁ is the intersection graph of the subsets and G₂ is the intersection graph of their complements. We also consider several special cases and explore bounds on the size of the universal set. © 1999 John Wiley & Sons, Inc. J Graph Theory 32: 171–190, 1999     

Application of bases to the study of measures and operators on measure spaces

Summary Under investigation are measures m defined on a σ-algebraA with range in a Banach space X having a Schauder basis {x_n}. Utilizing the corresponding coefficient functionals and coefficient measures, we study the interaction between properties for these measures and properties for the existing measure m. For the spaceCA(A, X) of all countably additive measures of finite variation fromA into X, we show that certain separable subspaces of it are isomorphic-isometric with certain separable subspaces of functions of bounded variation on the interval [0, 1]. For {v_n} inCA(A, X) such that {v_n(A)} converges to v(A) for all A εA a certain ? control measure ? is constructed. An integral for set functions relative to a measure is defined and necessary and sufficient conditions are given for weak convergence. Bounded operators on the space FAC(A,R) of finitelly additive scalar valued set functions onA which are absolutely continuous with respect to λ are considered. Necessary and sufficient conditions for continuity and for compactness are given for Banach space valued operators T defined on such spaces. Weak compactness of T is also studied. Finally, a different kind of representation is given for Banach space valued operators defined on the space FA_v(A, X) of finitely additive set functions fromA into X. Entrata in Redazione il 26 novembre 1976. The first author expresses his gratitude to the Italian Consiglio Nazionale delle Ricerche and the Università degli Studi di Param for the support of his work during his tenure as Visiting Professor of Mathematics. This work was supported by NATO Research Grant No. 835.     

On some inequalities of probabilistic number theory

Let Q ₊ denote the set of positive rational numbers. We define discrete probability measures ν _x on the σ-algebra of subsets of Q ₊.We introduce additive functions ƒ: Q ₊ → G and obtain a bound for ν_x(ƒ (r) ∉ X+X−X) using a probability related to some independent random variables. This inequality is an analogue to that proved by I. Ruzsa for additive arithmetical functions. Published in Lietuvos Matematikos Rinkinys, Vol. 46, No. 2, pp. 256–266, April–June, 2006.     

Percolation for the vacant set of random interlacements

We investigate random interlacements on ?^d, d ≥ 3. This model, recently introduced in [8], corresponds to a Poisson cloud on the space of doubly infinite trajectories modulo time shift tending to infinity at positive and negative infinite times. A nonnegative parameter u measures how many trajectories enter the picture. Our main interest lies in the percolative properties of the vacant set left by random interlacements at level u. We show that for all d ≥ 3 the vacant set at level u percolates when u is small. This solves an open problem of [8], where this fact has only been established when d ≥ 7. It also completes the proof of the nondegeneracy in all dimensions d ≥ 3 of the critical parameter u_* of [8]. © 2008 Wiley Periodicals, Inc.     

Differentiation in the branges spaces and embedding theorems

The boundedness conditions for the differentiation operator in Hilbert spaces of entire functions (Branges spaces) and conditions under which the embedding K_и⊂L₂(μ) holds in spaces K_и associated with the Branges spacesH(E) are studied. Measure μ such that the above embedding is isometric are of special interest. It turns out that the condition E'/E∈H^∞(C⁺) is sufficient for the boundedness of the differentiation operator inH(E). Under certain restrictions on E, this condition is also necessary. However, this fact fails in the general case, which is demonstrated by the counterexamples constructed in this paper. The convex structure of the set of measures μ such that the embedding K_E ^* _/E⊂L²(μ) is isometric (the set of such measures was described by de Brages) is considered. Some classes of measures that are extreme points in the set of Branges measures are distinguished. Examples of measures that are not extreme points are also given. Bibliography: 7 titles. Translated fromProblemy Matematicheskogo Analiza, No. 19, 1999, pp. 27–68.     

On the equivalence of three potential principles for right Markov processes

Summary We examine three of the principles of probabilistic potential theory in a nonclassical setting. These are: (i) the bounded maximum principle, (ii) the positive definiteness of the energy (of measures of bounded potential), and (iii) the condition that each semipolar set is polar. These principles are known to be equivalent in the context of two Markov processes in strong duality, when excessive functions are lower semicontinuous. We show that when the principles are appropriately formulated their equivalence persists in the wider context of a Borel right Markov processX with distinguished excessive measurem. We make no duality hypotheses andm need not be a reference measure. Our main tools are the stationary process (Y, Q _m) associated withX andm, and a correspondence between potentials U and certain random measures over (Y, Q _m).Research supported in part by NSF Grant 8419377     

Large Deviations for Brownian Intersection Measures

We consider p independent Brownian motions in \input amssym ${\Bbb R}^d$ . We assume that p ≥ 2 and p (d ? 2) < d. Let ?_t denote the intersection measure of the p paths by time t, i.e., the random measure on \input amssym ${\Bbb R}^d$ that assigns to any measurable set \input amssym $A \subset {\Bbb R}^d$ the amount of intersection local time of the motions spent in A by time t. Earlier results of X. Chen derived the logarithmic asymptotics of the upper tails of the total mass \input amssym $\ell _t \left({{\Bbb R}^d } \right)$ as t → ∞. In this paper, we derive a large‐deviation principle for the normalized intersection measure t^?p?_t on the set of positive measures on some open bounded set \input amssym $B \subset {\Bbb R}^d$ as t → ∞ before exiting B. The rate function is explicit and gives some rigorous meaning, in this asymptotic regime, to the understanding that the intersection measure is the pointwise product of the densities of the normalized occupation times measures of the p motions. Our proof makes the classical Donsker‐Varadhan principle for the latter applicable to the intersection measure. A second version of our principle is proved for the motions observed until the individual exit times from B, conditional on a large total mass in some compact set . This extends earlier studies on the intersection measure by König and Mörters. © 2012 Wiley Periodicals, Inc.     

Sets that are connected in two random graphs

–We consider two random graphs G₁, G₂, both on the same vertex set. We ask whether there is a non‐trivial set of vertices S, so that S induces a connected subgraph both in G₁ and in G₂. We determine the threshold for the appearance of such a subset, as well as the size of the largest such subset. © 2013 Wiley Periodicals, Inc. Random Struct. Alg., 45, 498–512, 2014     

Embedding into l ∞2 Is Easy, Embedding into l ∞3 Is?NP-Complete

We give a new algorithm for enumerating all possible embeddings of a metric space (i.e., the distances between every pair within a set of n points) into ℝ² Cartesian space preserving their l _∞ (or l ₁) metric distances. Its expected time is (i.e., within a poly-log of the size of the input) beating the previous algorithm. In contrast, we prove that detecting l _∞³ embeddings is NP-complete. The problem is also NP-complete within l ₁² or l _∞² with the added constraint that the locations of two of the points are given or alternatively that the two dimensions are curved into a three-dimensional sphere. We also refute a compaction theorem by giving a metric space that cannot be embedded in l _∞³; however, it can be embedded if any single point is removed. This research is partially supported by NSERC grants. I would like to thank Steven Watson for his extensive help on this paper.     

Some Remarks on Normal Measures and Measurable Cardinals

We prove two theorems which in a certain sense show that the number of normal measures a measurable cardinal κ can carry is independent of a given fixed behavior of the continuum function on any set having measure 1 with respect to every normal measure over κ . First, starting with a model V ⊨ “ZFC + GCH + o(κ) = δ*” for δ* ≤ κ⁺ any finite or infinite cardinal, we force and construct an inner model N ⊆ V [G] so that N ⊨ “ZF + (∀δ < κ) [DC_δ] + ¬AC_κ + κ carries exactly δ* normal measures + 2^δ = δ⁺⁺ on a set having measure 1 with respect to every normal measure over κ”. There is nothing special about 2^δ = δ here, and other stated values for the continuum function will be possible as well. Then, starting with a modelV ⊨ “ZFC + GCH + κis supercompact”, we force and construct models of AC in which, roughly speaking, regardless of the specified behavior of the continuum function below κ on any set having measure 1 with respect to every normal measure over κ, κ can in essence carry any number of normal measures δ* ≥ κ⁺⁺.