On nonregular ideals and <Emphasis Type="Italic">z</Emphasis>°-ideals in <Emphasis Type="Italic">C</Emphasis>(<Emphasis Type="Italic">X</Emphasis>)

The spaces X in which every prime z°-ideal of C(X) is either minimal or maximal are characterized. By this characterization, it turns out that for a large class of topological spaces X, such as metric spaces, basically disconnected spaces and one-point compactifications of discrete spaces, every prime z°-ideal in C(X) is either minimal or maximal. We will also answer the following questions: When is every nonregular prime ideal in C(X) a z°-ideal? When is every nonregular (prime) z-ideal in C(X) a z°-ideal? For instance, we show that every nonregular prime ideal of C(X) is a z°-ideal if and only if X is a ?-space (a space in which the boundary of any zeroset is contained in a zeroset with empty interior).     

Different prime <Emphasis Type="Italic">N</Emphasis>-ideals and IFP <Emphasis Type="Italic">N</Emphasis>-Ideals

We provide some characterizations of completely prime (completely semiprime) and 3-prime (3-semiprime) N-groups. The relationship between a 3-prime (completely prime) N-ideal P of an N-group Γ and the ideal (P: Γ) of the near-ring N is investigated. Moreover, the notion of IFP N-ideal is defined. We prove that the concept of IFP N-ideal occurs naturally where N is a left permutable (left self distributive, subcommutative) near-ring and Γ a monogenic N-group. Also, we obtain some relationships between an IFP N-ideal P of an N-group Γ and the ideal (P: Γ) of the near-ring N.     

Real <Emphasis Type="Italic">K</Emphasis>3 surfaces without real points,equivariant determinant of the Laplacian,and the Borcherds Φ-function

We consider an equivariant analogue of a conjecture of Borcherds. Let (Y, σ) be a real K3 surface without real points. We shall prove that the equivariant determinant of the Laplacian of (Y, σ) with respect to a σ-invariant Ricci-flat Kähler metric is expressed as the norm of the Borcherds Φ-function at the “period point”. Here the period of (Y, σ) is not the one in algebraic geometry.     

A certain clifford-like algebra and quantum vertex algebras

We show a new game characterizing various types of σ-porosity for Souslin sets in terms of winning strategies. We use the game to prove and reprove some new and older inscribing theorems for σ-ideals of σ-porous type in locally compact metric spaces.     

A General Approach to Isolating Roots of a Bitstream Polynomial

We describe a new approach to isolate the roots (either real or complex) of a square-free polynomial F with real coefficients. It is assumed that each coefficient of F can be approximated to any specified error bound and refer to such coefficients as bitstream coefficients. The presented method is exact, complete and deterministic. Compared to previous approaches (Eigenwillig in Real root isolation for exact and approximate polynomials using Descartes’ rule of signs, PhD thesis, Universität des Saarlandes, 2008; Eigenwillig et al. in CASC, LNCS, 2005; Mehlhorn and Sagraloff in J. Symb. Comput. 46(1):70–90, 2011) we improve in two aspects. Firstly, our approach can be combined with any existing subdivision method for isolating the roots of a polynomial with rational coefficients. Secondly, the approximation demand on the coefficients and the bit complexity of our approach is considerably smaller. In particular, we can replace the worst-case quantity σ(F) by the average-case quantity \({\prod_{i=1}^n\sqrt[n] {\sigma_i}}\) , where σ _i denotes the minimal distance of the i -th root ξ _i of F to any other root of F, σ(F) := min _i σ _i , and n = deg F. For polynomials with integer coefficients, our method matches the best bounds known for existing practical algorithms that perform exact operations on the input coefficients.     

Feller Generators with Measure-valued Drifts

We construct a L ^p -strong Feller process associated with the formal differential operator ? Δ + σ ?? on \(\mathbb R^{d}\), \(d \geqslant 3\), with drift σ in a wide class of measures (e.g. the sum of a measure having density in weak L ^d space and a Kato class measure), by exploiting a quantitative dependence of the smoothness of the domain of an operator realization of ? Δ + σ ?? generating a holomorphic C ₀-semigroup on \(L^{p}(\mathbb R^{d})\), p > d ? 1, on the value of the relative bound of σ.     

Commutators of homogeneous fractional integrals on Herz-type Hardy spaces with variable exponent

Let Ω ∈ L ^s (S ^n?1), s ≥ 1, be a homogeneous function of degree zero, and let σ (0 < σ < n) and b be Lipschitz or BMO functions. In this paper, we establish the boundedness of the commutators [b, T _Ω,σ ], generated by a homogeneous fractional integral operator T _Ω,σ and function b, on the Herz-type Hardy spaces with variable exponent.     

The Kreps-Yan theorem for Banach ideal spaces

Consider a closed convex cone C in a Banach ideal space X on some measure space with σ-finite measure. We prove that the fulfilment of the conditions C∩X ₊ = {0} and C??X ₊ guarantees the existence of a strictly positive continuous functional on X whose restriction to C is nonpositive.     

The Shape of Orthogonal Cycles in Three Dimensions

Let σ be a directed cycle whose edges have each been assigned a desired direction in 3D (East, West, North, South, Up, or Down) but no length. We say that σ is a shape cycle. We consider the following problem. Does there exist an orthogonal representation Γ of σ in 3D space such that no two edges of Γ intersect except at common endpoints and such that each edge of Γ has the direction specified in σ? If the answer is positive, we say that σ is simple. This problem arises in the context of extending orthogonal graph drawing techniques from 2D to 3D. We give a combinatorial characterization of simple shape cycles that yields linear time recognition and drawing algorithms.     

LIFTING DIFFERENTIABLE CURVES FROM ORBIT SPACES

Let ρ: G → O(V) be a real finite dimensional orthogonal representation of a compact Lie group, let σ = (σ ₁, ?, σn): V → ? ⁿ , where σ ₁, ?, σn n form a minimal system of homogeneous generators of the G-invariant polynomials on V, and set d = max_i deg σ _i . We prove that for each C ^d?1,1-curve c in σ(V) ?? ⁿ there exits a locally Lipschitz lift over σ, i.e., a locally Lipschitz curve \( \overline{c} \) in V so that c = σ ° \( \overline{c} \), and we obtain explicit bounds for the Lipschitz constant of \( \overline{c} \) in terms of c. Moreover, we show that each C ^d -curve in σ(V) admits a C ¹-lift. For finite groups G we deduce a multivariable version and some further results.     

Finite Groups with Given Weakly <Emphasis Type="Italic">σ</Emphasis>-Permutable Subgroups

Let G be a finite group and let σ = {σ _i | i ∈ I} be a partition of the set of all primes P. A set ? of subgroups of G is said to be a complete Hall σ-set of G if each nonidentity member of ? is a Hall σ _i -subgroup of G and ? has exactly one Hall σ _i -subgroup of G for every σ _i ∈ σ(G). A subgroup H of G is said to be σ-permutable in G if G possesses a complete Hall σ-set ? such that HA ^x = A ^x H for all A ∈ ? and all x ∈ G. A subgroup H of G is said to be weakly σ-permutable in G if there exists a σ-subnormal subgroup T of G such that G = HT and H ∩ T ≤ H _σG , where H _σG is the subgroup of H generated by all those subgroups of H which are σ-permutable in G. We study the structure of G under the condition that some given subgroups of G are weakly σ-permutable in G. In particular, we give the conditions under which a normal subgroup of G is hypercyclically embedded. Some available results are generalized.     

Finite groups with given σ-embedded and σ-n-embedded subgroups

Let G be a finite group and σ = {σ _i |i∈I} be a partition of the set of all primes P. A set H of subgroups of G is said to be a complete Hall σ-set of G if every non-identity member of H is a Hall σ _i -subgroup of G and H contains exactly one Hall σ _i -subgroup of G for every σ _i ∈ σ(G). A subgroup H is said to be σ-permutable if G possesses a complete Hall σ-set H such that HA ^x = A ^x H for all A ∈ H and all x ∈ G. Let H be a subgroup of G. Then we say that: (1) H is σ-embedded in G if there exists a σ-permutable subgroup T of G such that HT = H ^σG and H ∩ T ≤ H _σG , where H _σG is the subgroup of H generated by all those subgroups of H which are σ-permutable in G, and H ^σG is the σ-permutable closure of H, that is, the intersection of all σ-permutable subgroups of G containing H. (2) H is σ-n-embedded in G if there exists a normal subgroup T of G such that HT = H ^G and H ∩ T ≤ H _σG . In this paper, we study the properties of the new embedding subgroups and use them to determine the structure of finite groups.     

A mapping method in inverse Sturm-Liouville problems with singular potentials

In the space L ₂[0, π], the Sturm-Liouville operator L _D(y) = ?y″ + q(x)y with the Dirichlet boundary conditions y(0) = y(π) = 0 is analyzed. The potential q is assumed to be singular; namely, q = σ′, where σ ∈ L ₂[0, π], i.e., q ∈ W ₂ ^?1 [0, π]. The inverse problem of reconstructing the function σ from the spectrum of the operator L _D is solved in the subspace of odd real functions σ(π/2 ? x) = ?σ(π/2 + x). The existence and uniqueness of a solution to this inverse problem is proved. A method is proposed that allows one to solve this problem numerically.     

Heavy Tailed Approximate Identities and <Emphasis Type="Italic">σ</Emphasis>-stable Markov Kernels

The aim of this paper is to present some results relating the properties of stability, concentration and approximation to the identity of convolution through not necessarily mollification type families of heavy tailed Markov kernels. A particular case is provided by the kernels K _t obtained as the t mollification of L ^σ(t) selected from the family \(\mathcal {L}=\{L^{\sigma }: \widehat {L^{\sigma }}{(\xi )=e^{-|{\xi }|}}^{\sigma }, 0<\sigma <2\}\), by a given function σ with values in the interval (0,2). We show that a basic Harnack type inequality, introduced by C. Calderón in the convolution case, becomes at once natural to the setting and useful to connect the concepts of stability, concentration and approximation of the identity. Some of the general results are extended to spaces of homogeneous type since most of the concepts involved in the theory are given in terms of metric and measure.     

Julia set of λ exp(<Emphasis Type="Italic">z</Emphasis>)/<Emphasis Type="Italic">z</Emphasis> with real parameters λ

In this paper, we investigate the Julia set of the family λ exp(z)/z with real parameters λ. We look for what values of real parameters λ such that the Julia set of λ exp(z)/z does not coincide with the whole plane, and thus gives a complete classification for real parameters, which is similar to Jang’s result of a family of transcendental entire functions. Moreover, We also discuss the shape and size of Fatou sets and Julia sets of λ exp(z)/z with real parameters λ when the Julia sets are not the whole plane.     

Abelian varieties over large algebraic fields with infinite torsion

Let A be a non-zero abelian variety defined over a number field K and let \(\overline K \) be a fixed algebraic closure of K. For each element σ of the absolute Galois group \({\text{Gal}}(\overline K /K)\), let \(\overline K (\sigma )\) be the fixed field in \(\overline K \) of σ. We show that the torsion subgroup of \(A(\overline K (\sigma ))\) is infinite for all \(\sigma \in {\text{Gal}}(\overline K /K)\) outside of some set of Haar measure zero. This proves the number field case of a conjecture of W.-D. Geyer and M. Jarden.     

Positive Presentations of Families Relative to <Emphasis Type="Italic">e</Emphasis>-Oracles

We introduce the notion of A-numbering which generalizes the classical notion of numbering. All main attributes of classical numberings are carried over to the objects considered here. The problem is investigated of the existence of positive and decidable computable A-numberings for the natural families of sets e-reducible to a fixed set. We prove that, for every computable A-family containing an inclusion-greatest set, there also exists a positive computable A-numbering. Furthermore, for certain families we construct a decidable (and even single-valued) computable total A-numbering when A is a low set; we also consider a relativization containing all cases of total sets (this in fact corresponds to computability with a usual oracle).