Generalizations of a discrete universality theorem for Hurwitz zeta-functions

It is well known that the Hurwitz zeta-function ζ(s, α) with transcendental or rational parameter α is universal in the sense that the shifts ζ(s + iτ ), t ? \mathbbR \tau \in \mathbb{R} (continuous case), and ζ(s + imh), m ? \mathbbN è{ 0 } m \in \mathbb{N} \cup \left\{ 0 \right\} , with fixed h > 0 (discrete case) approximate any analytic function. In the paper, the discrete universality is extended for some classes of the functions F(ζ(s, α)).     

An extension of Hawkes theorem on the Hausdorff dimension of a Galton–Watson tree

Let ? be the genealogical tree of a supercritical multitype Galton–Watson process, and let Λ be the limit set of ?, i.e., the set of all infinite self-avoiding paths (called ends) through ? that begin at a vertex of the first generation. The limit set Λ is endowed with the metric d(ζ, ξ) = 2 ⁻ⁿ where n = n(ζ, ξ) is the index of the first generation where ζ and ξ differ. To each end ζ is associated the infinite sequence Φ(ζ) of types of the vertices of ζ. Let Ω be the space of all such sequences. For any ergodic, shift-invariant probability measure μ on Ω, define Ω_μ to be the set of all μ-generic sequences, i.e., the set of all sequences ω such that each finite sequence v occurs in ω with limiting frequency μ(Ω(v)), where Ω(v) is the set of all ω′?Ω that begin with the word v. Then the Hausdorff dimension of Λ∩Φ⁻¹ (Ω_μ) in the metric d is

Osservazioni su alcuni operatori ibridi iperbolico-ipoellittici

Riassunto Viene dimostrata l'equivalenza di alcune condizioni sul polinomio a coefficienti costantiP(ζ). La prima (si vedaH?rmander [3]), garantisce l'esistenza di una soluzione fondamentale diP(D) con supporto singolare in un cono convesso; l'ultima esprime il carattere ibrido diP(ζ). Viene infine costruita una soluzione fondamentale ultradistribuzione per un operatore 1/β-iperbolico-1/α-ipoellittico estendendo un precedente risultato [5] dell'autore.

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Summary The equivalence of some conditions on the polynomialP(ζ) with constant coefficients is proved. The first one (seeH?rmander [3]), implies the existence of a fundamental solution forP(D) with singular support contained in a convex cone; the last one shows thatP(ζ) is an hyperbolic-hypoelliptic polynomial. Finally an ultradistribution fundamental solution for a 1/β-hyperbolic-1/α-hypoelliptic operator is constructed, so extending a previous result [5] of the author.

     

A generalized square of the zeta function. Spectral decompositions

The spectral decomposition for the square of the classical Riemann zeta function ζ²(s) is generalized to the case of the product of two such functions ζ(s₁) · ζ(s₂) of different arguments. Bibliography: 6 titles. __________ Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 322, 2005, pp. 17–44.     

On the distribution of values of the derivative of the Riemann zeta function at its zeros. I

Let ζ′(s) be the derivative of the Riemann zeta function ζ(s). A study on the value distribution of ζ′(s) at the non-trivial zeros ρ of ζ(s) is presented. In particular, for a fixed positive number X, an asymptotic formula and a non-trivial upper bound for the sum Σ_{0<Im ρ≤T} ζ′(ρ)X ^ρ as T → ∞ are given. We clarify the dependence on the arithmetic nature of X.     

Defect Functions of Holomorphic Contractive Operator Functions and the Scattering Suboperator through the Internal Channels of a System. Part I

Let θ(ζ) be a Schur operator function, i.e., it is defined and holomorphic on the unit disk := C : 1 {\mathbb {D} := \{\zeta \in \mathbb {C} : \vert\zeta\vert < 1 \}} and its values are contractive operators acting from one Hilbert space into another one. In the first part of the paper the outer and *-outer Schur operator functions j(z){\varphi(\zeta)} and ψ(ζ) which describe respectively the deviations of the function θ(ζ) from inner and *-inner operator functions are studied. If j(z) 1 0{\varphi(\zeta)\neq 0} , then it means that in the scattering system for which θ(ζ) is the transfer function a portion of “information” comes inward the system and does not go outward, i.e., it is left in the internal channels of the system (Sect. 6). The function ψ(ζ) has the analogous property for the dual system. For this reason these functions are called the defect functions of the function θ(ζ). The explicit form of the defect functions j(z){\varphi(\zeta)} and ψ(ζ) is obtained and the analytic connection of these functions with the function θ(ζ) is described (Sects. 3, 5). The operator functions (l j(z)q(z)){\left(\begin{array}{l} \varphi(\zeta)\\ \theta(\zeta)\end{array}\right)} and (ψ(ζ), θ(ζ)) are Schur functions as well (Sect. 3). It is important that there exists the unique contractive measurable operator function χ(t), t ? ?\mathbb D{t\in\partial\mathbb {D}} , such that the operator function (l c(t)    j(t)y(t)    q(t) ){\left(\begin{array}{l} \chi(t)\quad \varphi(t)\\ \psi(t)\quad \theta(t) \end{array}\right)} , t ? ?\mathbb D,{t\in\partial\mathbb {D},} is also contractive (Part II, Sect. 12). The second part of the paper is devoted to studying the properties of the function χ(t). Specifically, it is shown that the function χ(t) is the scattering suboperator through the internal channels of the scattering system for which θ(ζ) is the transfer function (Part II, Sect. 12).     

Properties of Riesz fractional derivatives for Korteweg–de Vries solitons

Riesz fractional derivatives are defined as fractional powers of the Laplacian, D ^α  = (?Δ) ^α/2 for ${\alpha \in \mathbb{R}}Riesz fractional derivatives are defined as fractional powers of the Laplacian, D ^α  = (−Δ) ^α/2 for a ? \mathbbR{\alpha \in \mathbb{R}}. For the soliton solution of the Korteweg–de Vries equation, u ₀(X) with X = x − 4t, these derivatives, u _α (X) = D ^α u ₀(X), and their Hilbert transforms, v _α (X) = −HD ^α u ₀(X), can be expressed in terms of the full range Hurwitz Zeta functions ζ₊(s, a) and ζ₋(s, a), respectively. New properties are established for u _α (X) and v _α (X). It is proved that the functions w _α (X) = u _α (X) + iv _α (X) with α > −1 are solutions of the differential equation

-\fracddX(Pa(X)\fracdwdX)+Qa(X)w = lra(X)w,       X ? \mathbbR,-\frac{\rm d}{{\rm d}X}\left(P_{\alpha}(X)\frac{{\rm d}w}{{\rm d}X}\right)+Q_{\alpha}(X)w = \lambda\rho_{\alpha}(X)w,\qquad X \in \mathbb{R},      8. Infinite injective transformations whose centralizers have simple structure      Janusz Konieczny 《Central European Journal of Mathematics》2011,9(1):23-35 For an infinite set X, denote by Γ(X) the semigroup of all injective mappings from X to X under function composition. For α ∈ Γ(X), let C(α) = {β ∈ g/g(X): αβ = βα} be the centralizer of α in Γ(X). The aim of this paper is to determine those elements of Γ(X) whose centralizers have simple structure. We find α ∈ (X) such that various Green's relations in C(α) coincide, characterize α ∈ Γ(X) such that the $ \mathcal{J} $ \mathcal{J} -classes of C(α) form a chain, and describe Green's relations in C(α) for α with so-called finite ray-cycle decomposition. If α is a permutation, we also find the structure of C(α) in terms of direct and wreath products of familiar semigroups.      9. Notes on combinatorial set theory   总被引：1，自引：0，他引：1   Saharon Shelah 《Israel Journal of Mathematics》1973,14(3):262-277 We shall prove some unconnected theorems: (1) (G.C.H.) \omega _{\alpha + 1} \to \left( {\omega _\alpha + \xi } \right)_2^2 when ℵα is regular, │ξ│+<ωα. (2) There is a Jonsson algebra in ℵα+n, and \aleph _{a + n} \not \to \left[ {\aleph _{a + n} } \right]_{\aleph _{a + n} }^{n + 1} if 2^{\aleph _{ - - } } = \aleph _{a + n} \cdot (3) If λ>ℵ0 is a strong limit cardinal, then among the graphs with ≦λ vertices each of valence <λ there is a universal one. (4)(G.C.H.) If f is a set mapping on \omega _{a + 1} (ℵα regular) │f(x)∩f(y│<ℵα, then there is a free subset of order-type ζ for every ζ<ωα+1.      10. Self-similar extremal processes      E. I. Pancheva 《Journal of Mathematical Sciences》1998,92(3):3911-3920 Given an extremal process X: [0,∞)→[0,∞)d with lower curve C and associated point process N={(tk, Xk):k≥0}, tk distinct and Xk independent, given a sequence ζ n =(τ n , ξ n ), n≥1, of time-space changes (max-automorphisms of [0,∞)d+1), we study the limit behavior of the sequence of extremal processes Yn(t)=ξ n -1 ○ X ○ τn(t)=Cn(t) V max {ξ n -1 ○ Xk: tk ≤ τn(t){ ⇒ Y under a regularity condition on the norming sequence ζn and asymptotic negligibility of the max-increments of Yn. The limit class consists of self-similar (with respect to a group ηα=(σα, Lα), α>0, of time-space changes) extremal processes. By self-similarity here we mean the property Lα ○ Y(t) = d Y ○ αα(t) for all α>0. The univariate marginals of Y are max-self-decomposable. If additionally the initial extremal process X is assumed to have homogeneous max-increments, then the limit process is max-stable with homogeneous max-increments. Supported by the Bulgarian Ministry of Education and Sciences (grant No. MM 234/1996). Proceedings of the Seminar on Stability Problems for Stochastic Models, Hajdúszoboszló, Hungary, 1997, Part I.      11. Cyclotomic units over finite fields      Klaus Hoechsmann 《Rendiconti del Circolo Matematico di Palermo》1995,44(1):5-20 Let ζ be a primitivesp-th root of unity for a primep>2, and consider the group Ω(ζ) of cyclotomic units in the ringR(ζ)=ℒ[ζ+ζ-1]. This paper deals with the image of Ω(ζ) in the unit group ofR(ζ)/qR(ζ), whereq is a prime ≠p. In particular, it obtains criteria for this image to be essentially everything, and a lower bound on the density of primesp (withq fixed) for which it cannot be. These results have a direct bearing on previous work about units in integral group rings for cyclic groups of orderpq. Work supported in part by an operating grant from NSERC (Canada).      12. Sui commutatori di alcuni operatori pseudo-differenziali      S. Zaidman 《Annali dell'Universita di Ferrara》1968,13(1):33-36 Riassunto Nel presente lavoro si considera una classe di simboli non-omogenei, più generale di quella introdotta nel [3]; per operatori pseudo-differenzialiEl(x,D) associati a tali simboli si considera il commutatore con l'operatore di Friedrichs Ψ(D) associato a una funzione Ψ(ξ) che gode di alcune speciali proprietà; prendendo inoltre una funzione ζ(ξ) nulla per ∣≤∣⩽1/2 e=1 per |ξ|≥1, si dimostra usando una tecnica dovuta a H?rmander [1] che l'operatore ζ(D)[Ψ(D),El(x,D)] è di ordine ≤-1/2. Résumé Dans ce travail on considère une classe de symboles non-homogènes plus générale de celle introduite dans [3]; pour les opérateurs pseudo-différentielsEl(x,D) associés à tels symboles on considère le commutateur [Ψ(D),El(x,D)] avec l'opérateur de Friedrichs Ψ(D) associé à une fonction Ψ(ξ) jouissant de certaines propriétés spéciales. En prenant ensuite une fonction ζ(ξ) nulle pour ∣≤∣⩽1/2 e=1 et =1 pour |ξ|≥1, on démontre avec une technique de H?rmander [1] que l'opérateur ζ(D)[Ψ(D),El(x,D)] est d'ordre ≤-1/2.       13. On the degree of continuity and smoothness of sine and cosine Fourier transforms of Lebesgue integrable functions      Ferenc Móricz 《Acta Mathematica Hungarica》2012,134(3):356-368 We consider complex-valued functions f∈L 1(ℝ+), where ℝ+:=[0,∞), and prove sufficient conditions under which the sine Fourier transform [^(f)]s\hat{f}_{s} and the cosine Fourier transform [^(f)]c\hat{f}_{c} belong to one of the Lipschitz classes Lip (α) and lip (α) for some 0<α≦1, or to one of the Zygmund classes Zyg (α) and zyg (α) for some 0<α≦2. These sufficient conditions are best possible in the sense that they are also necessary if f(x)≧0 almost everywhere.      14. Almost linear upper bounds on the length of general davenport—schinzel sequences      Micha Sharir 《Combinatorica》1987,7(1):131-143 Davenport—Schinzel sequences are sequences that do not contain forbidden subsequences of alternating symbols. They arise in the computation of the envelope of a set of functions. We obtain almost linear upper bounds on the length λs(n) of Davenport—Schinzel sequences composed ofn symbols in which no alternating subsequence is of length greater thans+1. These bounds are of the formO(nα(n)O(α(n)5-3)), and they generalize and extend the tight bound Θ(nα(n)) obtained by Hart and Sharir for the special cases=3 (α(n) is the functional inverse of Ackermann’s function), and also improve the upper boundO(n log*n) due to Szemerédi. Work on this paper has been supported in part by a grant from the U.S. — Israeli Binational Science Foundation.      15. Thompson’s conjecture for simple groups with connected prime graph      I. B. Gorshkov 《Algebra and Logic》2012,51(2):111-127 We deal with finite simple groups G with the property π(G) ⊆ {2, 3, 5, 7, 11, 13, 17}, where π(G) is the set of all prime divisors of the order of a group G. The set of all such groups is denoted by ζ 17. Thompson’s conjecture in [1, Question 12.38] is proved valid for all groups in ζ 17 whose prime graph is connected.      16. On a class of hyperbolic 3-orbifolds of small volume and small heegaard genus associated to 2-bridge links      Mattia Mecchia  Bruno Zimmermann 《Rendiconti del Circolo Matematico di Palermo》2000,49(1):41-60 We consider a class of hyperbolic 3-orbifoldsO(α/β); the underlying topological space of such an orbifold is the 3-sphere and the singular set is obtained by adding the two standard (upper and lower) unknotting tunnels to a 2-bridge linkL(α/β) (and associating branching order two to both unknotting tunnels). These 3-orbifolds are extremal with respect to the notion of Heegaard genus or Heegaard number of 3-orbifolds; it is to be expected that they are also extremal with respect to the volume, that is the smallest volume hyperbolic 3-orbifolds should belong to this or some closely related class. We show that an orbifoldO(α/β) has a uniqueD 2-covering by an orbifoldℒ n(α/β) wose space is the 3-sphere and whose singular set is the same 2-bridge linkL(α/β) used for the construction ofO(α/β); moreoverO(α/β) is hyperbolic if and only ifℒ n(α/β) is hyperbolic. As the volumes of the orbifoldsℒ n(α/β) are known resp. can be computed, this allows to compute the volumes of the orbifoldsO(α/β). The problem of computation of volumes remains open for some closely related classes of 3-orbifolds which are also extremal with respect to the Heegaard genus (for example associating a branching order bigger than two to one or both unknotting tunnels).      17. An explicit formula for the square of the Riemann zeta-function in the critical strip      Y. Sasaki 《Lithuanian Mathematical Journal》2007,47(3):311-326 In this article, we prove an explicit formula for |ζ(σ + iT)|2, where ζ(s) is the Riemann zeta-function and 1/2 < σ < 1, which is an analogue of Jutila’s formula. Our proof differs from that of Jutila. Published in Lietuvos Matematikos Rinkinys, Vol. 47, No. 3, pp. 381–398, July–September, 2007.      18. The negative discrete spectrum of the operator (-τ) l -αV inL 2(R d ) ford even and 2l≥dinL 2(R d ) ford even and 2l≥d      Mikhail Sh. Birman  Ari Laptev  Michael Solomyak 《Arkiv f?r Matematik》1997,35(1):87-126 We study the asymptotic behaviour ofN(α)—the number of negative eigenvalues of the operator (-τ) l -αV inL 2(R d ) for an evend and2l≥d. This is the only case where the previously known results were far from being complete. In order to describe our results we introduce an auxiliary ordinary differential operator (system) on the semiaxis. Depending on the spectral properties of this operator we can distinguish between three cases whereN(α) is of the Weyl-type,N(α) is of the Weyl-order but not the Weyl-type coefficient and finally whereN(α)=O(αq) withq>d/2l.      19. A sufficient degree condition for a graph to contain all trees of size <Emphasis Type="Italic">k</Emphasis>      Camino Balbuena  Alberto Márquez  José Ramón Portillo 《数学学报(英文版)》2011,27(1):135-140 The Erdős-Sós conjecture says that a graph G on n vertices and number of edges e(G) > n(k− 1)/2 contains all trees of size k. In this paper we prove a sufficient condition for a graph to contain every tree of size k formulated in terms of the minimum edge degree ζ(G) of a graph G defined as ζ(G) = min{d(u) + d(v) − 2: uv ∈ E(G)}. More precisely, we show that a connected graph G with maximum degree Δ(G) ≥ k and minimum edge degree ζ(G) ≥ 2k − 4 contains every tree of k edges if d G (x) + d G (y) ≥ 2k − 4 for all pairs x, y of nonadjacent neighbors of a vertex u of d G (u) ≥ k.      20. The centralizer of an element in a Lie algebra of type <Emphasis Type="Italic">L</Emphasis>      Caihui?Lu  Wenwu?ShaoEmail author 《中国科学A辑(英文版)》2004,47(6):854-861 In this paper, we investigate the Lie algebra L(A,α,δ) of type L and obtain the respective sufficient conditions for L(A,α,δ δ to be semisimple, and for Z(ω) = Fω as well, where 0 ≠ ω Є L(A, α, δ, δ) and Z(ω) is the centralizer of ω.

Infinite injective transformations whose centralizers have simple structure

For an infinite set X, denote by Γ(X) the semigroup of all injective mappings from X to X under function composition. For α ∈ Γ(X), let C(α) = {β ∈ g/g(X): αβ = βα} be the centralizer of α in Γ(X). The aim of this paper is to determine those elements of Γ(X) whose centralizers have simple structure. We find α ∈ (X) such that various Green's relations in C(α) coincide, characterize α ∈ Γ(X) such that the $ \mathcal{J} $ \mathcal{J} -classes of C(α) form a chain, and describe Green's relations in C(α) for α with so-called finite ray-cycle decomposition. If α is a permutation, we also find the structure of C(α) in terms of direct and wreath products of familiar semigroups.     

Notes on combinatorial set theory

We shall prove some unconnected theorems: (1) (G.C.H.) \omega _{\alpha + 1} \to \left( {\omega _\alpha + \xi } \right)_2^2 when ℵ_α is regular, │ξ│⁺<ωα. (2) There is a Jonsson algebra in ℵ_α+n, and \aleph _{a + n} \not \to \left[ {\aleph _{a + n} } \right]_{\aleph _{a + n} }^{n + 1} if 2^{\aleph _{ - - } } = \aleph _{a + n} \cdot (3) If λ>ℵ₀ is a strong limit cardinal, then among the graphs with ≦λ vertices each of valence <λ there is a universal one. (4)(G.C.H.) If f is a set mapping on \omega _{a + 1} (ℵ_α regular) │f(x)∩f(y│<ℵ_α, then there is a free subset of order-type ζ for every ζ<ω_α+1.     

Self-similar extremal processes

Given an extremal process X: [0,∞)→[0,∞)^d with lower curve C and associated point process N={(t_k, X_k):k≥0}, t_k distinct and X_k independent, given a sequence ζ _n =(τ _n , ξ _n ), n≥1, of time-space changes (max-automorphisms of [0,∞)^d+1), we study the limit behavior of the sequence of extremal processes Y_n(t)=ξ _n ^-1 ○ X ○ τ_n(t)=C_n(t) V max {ξ _n ^-1 ○ X_k: t_k ≤ τ_n(t){ ⇒ Y under a regularity condition on the norming sequence ζ_n and asymptotic negligibility of the max-increments of Y_n. The limit class consists of self-similar (with respect to a group η_α=(σ_α, L_α), α>0, of time-space changes) extremal processes. By self-similarity here we mean the property L_α ○ Y(t) ₌ ^d Y ○ α_α(t) for all α>0. The univariate marginals of Y are max-self-decomposable. If additionally the initial extremal process X is assumed to have homogeneous max-increments, then the limit process is max-stable with homogeneous max-increments. Supported by the Bulgarian Ministry of Education and Sciences (grant No. MM 234/1996). Proceedings of the Seminar on Stability Problems for Stochastic Models, Hajdúszoboszló, Hungary, 1997, Part I.     

Cyclotomic units over finite fields

Let ζ be a primitivesp-th root of unity for a primep>2, and consider the group Ω(ζ) of cyclotomic units in the ringR(ζ)=ℒ[ζ+ζ^-1]. This paper deals with the image of Ω(ζ) in the unit group ofR(ζ)/qR(ζ), whereq is a prime ≠p. In particular, it obtains criteria for this image to be essentially everything, and a lower bound on the density of primesp (withq fixed) for which it cannot be. These results have a direct bearing on previous work about units in integral group rings for cyclic groups of orderpq. Work supported in part by an operating grant from NSERC (Canada).     

Sui commutatori di alcuni operatori pseudo-differenziali

Riassunto Nel presente lavoro si considera una classe di simboli non-omogenei, più generale di quella introdotta nel [3]; per operatori pseudo-differenzialiEl(x,D) associati a tali simboli si considera il commutatore con l'operatore di Friedrichs Ψ(D) associato a una funzione Ψ(ξ) che gode di alcune speciali proprietà; prendendo inoltre una funzione ζ(ξ) nulla per ∣≤∣⩽1/2 e=1 per |ξ|≥1, si dimostra usando una tecnica dovuta a H?rmander [1] che l'operatore ζ(D)[Ψ(D),El(x,D)] è di ordine ≤-1/2.

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Résumé Dans ce travail on considère une classe de symboles non-homogènes plus générale de celle introduite dans [3]; pour les opérateurs pseudo-différentielsEl(x,D) associés à tels symboles on considère le commutateur [Ψ(D),El(x,D)] avec l'opérateur de Friedrichs Ψ(D) associé à une fonction Ψ(ξ) jouissant de certaines propriétés spéciales. En prenant ensuite une fonction ζ(ξ) nulle pour ∣≤∣⩽1/2 e=1 et =1 pour |ξ|≥1, on démontre avec une technique de H?rmander [1] que l'opérateur ζ(D)[Ψ(D),El(x,D)] est d'ordre ≤-1/2.

     

On the degree of continuity and smoothness of sine and cosine Fourier transforms of Lebesgue integrable functions

We consider complex-valued functions f∈L ¹(ℝ₊), where ℝ₊:=[0,∞), and prove sufficient conditions under which the sine Fourier transform [^(f)]_s\hat{f}_{s} and the cosine Fourier transform [^(f)]_c\hat{f}_{c} belong to one of the Lipschitz classes Lip (α) and lip (α) for some 0<α≦1, or to one of the Zygmund classes Zyg (α) and zyg (α) for some 0<α≦2. These sufficient conditions are best possible in the sense that they are also necessary if f(x)≧0 almost everywhere.     

Almost linear upper bounds on the length of general davenport—schinzel sequences

Davenport—Schinzel sequences are sequences that do not contain forbidden subsequences of alternating symbols. They arise in the computation of the envelope of a set of functions. We obtain almost linear upper bounds on the length λ_s(n) of Davenport—Schinzel sequences composed ofn symbols in which no alternating subsequence is of length greater thans+1. These bounds are of the formO(nα(n)^O(α(n)5-3)), and they generalize and extend the tight bound Θ(nα(n)) obtained by Hart and Sharir for the special cases=3 (α(n) is the functional inverse of Ackermann’s function), and also improve the upper boundO(n log*n) due to Szemerédi. Work on this paper has been supported in part by a grant from the U.S. — Israeli Binational Science Foundation.     

Thompson’s conjecture for simple groups with connected prime graph

We deal with finite simple groups G with the property π(G) ⊆ {2, 3, 5, 7, 11, 13, 17}, where π(G) is the set of all prime divisors of the order of a group G. The set of all such groups is denoted by ζ ₁₇. Thompson’s conjecture in [1, Question 12.38] is proved valid for all groups in ζ ₁₇ whose prime graph is connected.     

On a class of hyperbolic 3-orbifolds of small volume and small heegaard genus associated to 2-bridge links

We consider a class of hyperbolic 3-orbifoldsO(α/β); the underlying topological space of such an orbifold is the 3-sphere and the singular set is obtained by adding the two standard (upper and lower) unknotting tunnels to a 2-bridge linkL(α/β) (and associating branching order two to both unknotting tunnels). These 3-orbifolds are extremal with respect to the notion of Heegaard genus or Heegaard number of 3-orbifolds; it is to be expected that they are also extremal with respect to the volume, that is the smallest volume hyperbolic 3-orbifolds should belong to this or some closely related class. We show that an orbifoldO(α/β) has a uniqueD ₂-covering by an orbifoldℒ _n(α/β) wose space is the 3-sphere and whose singular set is the same 2-bridge linkL(α/β) used for the construction ofO(α/β); moreoverO(α/β) is hyperbolic if and only ifℒ _n(α/β) is hyperbolic. As the volumes of the orbifoldsℒ _n(α/β) are known resp. can be computed, this allows to compute the volumes of the orbifoldsO(α/β). The problem of computation of volumes remains open for some closely related classes of 3-orbifolds which are also extremal with respect to the Heegaard genus (for example associating a branching order bigger than two to one or both unknotting tunnels).     

An explicit formula for the square of the Riemann zeta-function in the critical strip

In this article, we prove an explicit formula for |ζ(σ + iT)|², where ζ(s) is the Riemann zeta-function and 1/2 < σ < 1, which is an analogue of Jutila’s formula. Our proof differs from that of Jutila. Published in Lietuvos Matematikos Rinkinys, Vol. 47, No. 3, pp. 381–398, July–September, 2007.     

The negative discrete spectrum of the operator (-τ) l -αV inL 2(R d ) ford even and 2l≥dinL 2(R d ) ford even and 2l≥d

We study the asymptotic behaviour ofN(α)—the number of negative eigenvalues of the operator (-τ) ^l -αV inL ₂(R ^d ) for an evend and2l≥d. This is the only case where the previously known results were far from being complete. In order to describe our results we introduce an auxiliary ordinary differential operator (system) on the semiaxis. Depending on the spectral properties of this operator we can distinguish between three cases whereN(α) is of the Weyl-type,N(α) is of the Weyl-order but not the Weyl-type coefficient and finally whereN(α)=O(α^q) withq>d/2l.     

A sufficient degree condition for a graph to contain all trees of size <Emphasis Type="Italic">k</Emphasis>

The Erdős-Sós conjecture says that a graph G on n vertices and number of edges e(G) > n(k− 1)/2 contains all trees of size k. In this paper we prove a sufficient condition for a graph to contain every tree of size k formulated in terms of the minimum edge degree ζ(G) of a graph G defined as ζ(G) = min{d(u) + d(v) − 2: uv ∈ E(G)}. More precisely, we show that a connected graph G with maximum degree Δ(G) ≥ k and minimum edge degree ζ(G) ≥ 2k − 4 contains every tree of k edges if d _G (x) + d _G (y) ≥ 2k − 4 for all pairs x, y of nonadjacent neighbors of a vertex u of d _G (u) ≥ k.     

The centralizer of an element in a Lie algebra of type <Emphasis Type="Italic">L</Emphasis>

In this paper, we investigate the Lie algebra L(A,α,δ) of type L and obtain the respective sufficient conditions for L(A,α,δ δ to be semisimple, and for Z(ω) = Fω as well, where 0 ≠ ω Є L(A, α, δ, δ) and Z(ω) is the centralizer of ω.