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1. CMB Online first

Parlier, Hugo
 A short note on short pants It is a theorem of Bers that any closed hyperbolic surface admits a pants decomposition consisting of curves of bounded length where the bound only depends on the topology of the surface. The question of the quantification of the optimal constants has been well studied and the best upper bounds to date are linear in genus, a theorem of Buser and SeppÃ¤lÃ¤. The goal of this note is to give a short proof of a linear upper bound which slightly improve the best known bound. Keywords:hyperbolic surfaces, geodesics, pants decompositionsCategories:30F10, 32G15, 53C22

2. CMB Online first

Fang, Zhong-Shan; Zhou, Ze-Hua
 New Characterizations of the Weighted Composition Operators Between Bloch Type Spaces in the Polydisk We give some new characterizations for compactness of weighted composition operators $uC_\varphi$ acting on Bloch-type spaces in terms of the power of the components of $\varphi,$ where $\varphi$ is a holomorphic self-map of the polydisk $\mathbb{D}^n,$ thus generalizing the results obtained by HyvÃ¤rinen and LindstrÃ¶m in 2012. Keywords:weighted composition operator, compactness, Bloch type spaces, polydisk, several complex variablesCategories:47B38, 47B33, 32A37, 45P05, 47G10

3. CMB 2012 (vol 57 pp. 97)

Levy, Jason
 Rationality and the Jordan-Gatti-Viniberghi decomposition We verify our earlier conjecture and use it to prove that the semisimple parts of the rational Jordan-Kac-Vinberg decompositions of a rational vector all lie in a single rational orbit. Keywords:reductive group, $G$-module, Jordan decomposition, orbit closure, rationalityCategories:20G15, 14L24

4. CMB 2012 (vol 56 pp. 606)

Mazorchuk, Volodymyr; Zhao, Kaiming
 Characterization of Simple Highest Weight Modules We prove that for simple complex finite dimensional Lie algebras, affine Kac-Moody Lie algebras, the Virasoro algebra and the Heisenberg-Virasoro algebra, simple highest weight modules are characterized by the property that all positive root elements act on these modules locally nilpotently. We also show that this is not the case for higher rank Virasoro and for Heisenberg algebras. Keywords:Lie algebra, highest weight module, triangular decomposition, locally nilpotent actionCategories:17B20, 17B65, 17B66, 17B68

5. CMB 2011 (vol 56 pp. 442)

Zelenyuk, Yevhen
 Closed Left Ideal Decompositions of $U(G)$ Let $G$ be an infinite discrete group and let $\beta G$ be the Stone--Äech compactification of $G$. We take the points of $Äta G$ to be the ultrafilters on $G$, identifying the principal ultrafilters with the points of $G$. The set $U(G)$ of uniform ultrafilters on $G$ is a closed two-sided ideal of $\beta G$. For every $p\in U(G)$, define $I_p\subseteq\beta G$ by $I_p=\bigcap_{A\in p}\operatorname{cl} (GU(A))$, where $U(A)=\{p\in U(G):A\in p\}$. We show that if $|G|$ is a regular cardinal, then $\{I_p:p\in U(G)\}$ is the finest decomposition of $U(G)$ into closed left ideals of $\beta G$ such that the corresponding quotient space of $U(G)$ is Hausdorff. Keywords:Stone--Äech compactification, uniform ultrafilter, closed left ideal, decompositionCategories:22A15, 54H20, 22A30, 54D80

6. CMB 2011 (vol 56 pp. 229)

Arvanitidis, Athanasios G.; Siskakis, Aristomenis G.
 CesÃ ro Operators on the Hardy Spaces of the Half-Plane In this article we study the CesÃ ro operator $$\mathcal{C}(f)(z)=\frac{1}{z}\int_{0}^{z}f(\zeta)\,d\zeta,$$ and its companion operator $\mathcal{T}$ on Hardy spaces of the upper half plane. We identify $\mathcal{C}$ and $\mathcal{T}$ as resolvents for appropriate semigroups of composition operators and we find the norm and the spectrum in each case. The relation of $\mathcal{C}$ and $\mathcal{T}$ with the corresponding Ces\`{a}ro operators on Lebesgue spaces $L^p(\mathbb R)$ of the boundary line is also discussed. Keywords:CesÃ ro operators, Hardy spaces, semigroups, composition operatorsCategories:47B38, 30H10, 47D03

7. CMB 2011 (vol 56 pp. 70)

Hrubeš, P.; Wigderson, A.; Yehudayoff, A.
 An Asymptotic Bound on the Composition Number of Integer Sums of Squares Formulas Let $\sigma_{\mathbb Z}(k)$ be the smallest $n$ such that there exists an identity $(x_1^2 + x_2^2 + \cdots + x_k^2) \cdot (y_1^2 + y_2^2 + \cdots + y_k^2) = f_1^2 + f_2^2 + \cdots + f_n^2,$ with $f_1,\dots,f_n$ being polynomials with integer coefficients in the variables $x_1,\dots,x_k$ and $y_1,\dots,y_k$. We prove that $\sigma_{\mathbb Z}(k) \geq \Omega(k^{6/5})$. Keywords:composition formulas, sums of squares, Radon-Hurwitz numberCategory:11E25

8. CMB 2011 (vol 55 pp. 697)

Borwein, Jonathan M.; Vanderwerff, Jon
 Constructions of Uniformly Convex Functions We give precise conditions under which the composition of a norm with a convex function yields a uniformly convex function on a Banach space. Various applications are given to functions of power type. The results are dualized to study uniform smoothness and several examples are provided. Keywords:convex function, uniformly convex function, uniformly smooth function, power type, Fenchel conjugate, composition, normCategories:52A41, 46G05, 46N10, 49J50, 90C25

9. CMB 2011 (vol 55 pp. 303)

Han, Yongsheng; Lee, Ming-Yi; Lin, Chin-Cheng
 Atomic Decomposition and Boundedness of Operators on Weighted Hardy Spaces In this article, we establish a new atomic decomposition for $f\in L^2_w\cap H^p_w$, where the decomposition converges in $L^2_w$-norm rather than in the distribution sense. As applications of this decomposition, assuming that $T$ is a linear operator bounded on $L^2_w$ and $0 Keywords:$A_p$weights, atomic decomposition, CalderÃ³n reproducing formula, weighted Hardy spacesCategories:42B25, 42B30 10. CMB 2011 (vol 55 pp. 441) Zorboska, Nina  Univalently Induced, Closed Range, Composition Operators on the Bloch-type Spaces While there is a large variety of univalently induced closed range composition operators on the Bloch space, we show that the only univalently induced, closed range, composition operators on the Bloch-type spaces$B^{\alpha}$with$\alpha \ne 1$are the ones induced by a disc automorphism. Keywords:composition operators, Bloch-type spaces, closed range, univalentCategories:47B35, 32A18 11. CMB 2009 (vol 53 pp. 278) Galego, Elói M.  Cantor-Bernstein Sextuples for Banach Spaces Let$X$and$Y$be Banach spaces isomorphic to complemented subspaces of each other with supplements$A$and$B$. In 1996, W. T. Gowers solved the Schroeder--Bernstein (or Cantor--Bernstein) problem for Banach spaces by showing that$X$is not necessarily isomorphic to$Y$. In this paper, we obtain a necessary and sufficient condition on the sextuples$(p, q, r, s, u, v)$in$\mathbb N$with$p+q \geq 1$,$r+s \geq 1$and$u, v \in \mathbb N^*$, to provide that$X$is isomorphic to$Y$, whenever these spaces satisfy the following decomposition scheme $$A^u \sim X^p \oplus Y^q, \quad B^v \sim X^r \oplus Y^s.$$ Namely,$\Phi=(p-u)(s-v)-(q+u)(r+v)$is different from zero and$\Phi$divides$p+q$and$r+s$. These sextuples are called Cantor--Bernstein sextuples for Banach spaces. The simplest case$(1, 0, 0, 1, 1, 1)$indicates the well-known PeÅczyÅski's decomposition method in Banach space. On the other hand, by interchanging some Banach spaces in the above decomposition scheme, refinements of the Schroeder--Bernstein problem become evident. Keywords:Pel czyÅski's decomposition method, Schroeder-Bernstein problemCategories:46B03, 46B20 12. CMB 2008 (vol 51 pp. 195) Chen, Huaihui; Gauthier, Paul  Boundedness from Below of Composition Operators on$\alpha$-Bloch Spaces We give a necessary and sufficient condition for a composition operator on an$\alpha$-Bloch space with$\alpha\ge 1$to be bounded below. This extends a known result for the Bloch space due to P. Ghatage, J. Yan, D. Zheng, and H. Chen. Keywords:Bloch functions, composition operatorsCategories:32A18, 30H05 13. CMB 2007 (vol 50 pp. 504) Dukes, Peter; Ling, Alan C. H.  Asymptotic Existence of Resolvable Graph Designs Let$v \ge k \ge 1$and$\lam \ge 0$be integers. A \emph{block design}$\BD(v,k,\lambda)$is a collection$\cA$of$k$-subsets of a$v$-set$X$in which every unordered pair of elements from$X$is contained in exactly$\lambda$elements of$\cA$. More generally, for a fixed simple graph$G$, a \emph{graph design}$\GD(v,G,\lambda)$is a collection$\cA$of graphs isomorphic to$G$with vertices in$X$such that every unordered pair of elements from$X$is an edge of exactly$\lambda$elements of$\cA$. A famous result of Wilson says that for a fixed$G$and$\lambda$, there exists a$\GD(v,G,\lambda)$for all sufficiently large$v$satisfying certain necessary conditions. A block (graph) design as above is \emph{resolvable} if$\cA$can be partitioned into partitions of (graphs whose vertex sets partition)$X$. Lu has shown asymptotic existence in$v$of resolvable$\BD(v,k,\lambda)$, yet for over twenty years the analogous problem for resolvable$\GD(v,G,\lambda)$has remained open. In this paper, we settle asymptotic existence of resolvable graph designs. Keywords:graph decomposition, resolvable designsCategories:05B05, 05C70, 05B10 14. CMB 2004 (vol 47 pp. 49) Lindström, Mikael; Makhmutov, Shamil; Taskinen, Jari  The Essential Norm of a Bloch-to-$Q_p$Composition Operator The$Q_p$spaces coincide with the Bloch space for$p>1$and are subspaces of$\BMOA$for$0 Keywords:Bloch space, little Bloch space, $\BMOA$, $\VMOA$, $Q_p$ spaces,, composition operator, compact operator, essential normCategories:47B38, 47B10, 46E40, 46E15

15. CMB 2003 (vol 46 pp. 356)

Ishiwata, Makiko; Przytycki, Józef H.; Yasuhara, Akira
 Branched Covers of Tangles in Three-balls We give an algorithm for a surgery description of a $p$-fold cyclic branched cover of $B^3$ branched along a tangle. We generalize constructions of Montesinos and Akbulut-Kirby. Keywords:tangle, branched cover, surgery, Heegaard decompositionCategories:57M25, 57M12

16. CMB 1999 (vol 42 pp. 139)

Bonet, José; Domański, Paweł; Lindström, Mikael
 Essential Norm and Weak Compactness of Composition Operators on Weighted Banach Spaces of Analytic Functions Every weakly compact composition operator between weighted Banach spaces $H_v^{\infty}$ of analytic functions with weighted sup-norms is compact. Lower and upper estimates of the essential norm of continuous composition operators are obtained. The norms of the point evaluation functionals on the Banach space $H_v^{\infty}$ are also estimated, thus permitting to get new characterizations of compact composition operators between these spaces. Keywords:weighted Banach spaces of holomorphic functions, composition operator, compact operator, weakly compact operatorCategories:47B38, 30D55, 46E15