Expand all Collapse all  Results 26  43 of 43 
26. CJM 2007 (vol 59 pp. 966)
Operator Amenability of the Fourier Algebra in the $\cb$Multiplier Norm Let $G$ be a locally compact group, and let $A_{\cb}(G)$ denote the
closure of $A(G)$, the Fourier algebra of $G$, in the space of completely
bounded multipliers of $A(G)$. If $G$ is a weakly amenable, discrete group
such that $\cstar(G)$ is residually finitedimensional, we show that
$A_{\cb}(G)$ is operator amenable. In particular,
$A_{\cb}(\free_2)$ is operator amenable even though $\free_2$, the free
group in two generators, is not an amenable group. Moreover, we show that
if $G$ is a discrete group such that $A_{\cb}(G)$ is operator amenable,
a closed ideal of $A(G)$ is weakly completely complemented in $A(G)$
if and only if it has an approximate identity bounded in the $\cb$multiplier
norm.
Keywords:$\cb$multiplier norm, Fourier algebra, operator amenability, weak amenability Categories:43A22, 43A30, 46H25, 46J10, 46J40, 46L07, 47L25 
27. CJM 2007 (vol 59 pp. 614)
Preduals and Nuclear Operators Associated with Bounded, $p$Convex, $p$Concave and Positive $p$Summing Operators 
Preduals and Nuclear Operators Associated with Bounded, $p$Convex, $p$Concave and Positive $p$Summing Operators We use Krivine's form of the Grothendieck inequality
to renorm the space of bounded linear maps acting between Banach
lattices. We
construct preduals and describe the nuclear operators
associated with these preduals for this renormed space
of bounded operators as well as for
the spaces of $p$convex,
$p$concave and positive $p$summing operators acting
between Banach lattices and Banach spaces.
The nuclear operators obtained are described in
terms of factorizations through
classical Banach spaces via positive operators.
Keywords:$p$convex operator, $p$concave operator, $p$summing operator, Banach space, Banach lattice, nuclear operator, sequence space Categories:46B28, 47B10, 46B42, 46B45 
28. CJM 2007 (vol 59 pp. 638)
Distance from Idempotents to Nilpotents We give bounds on the distance from a nonzero idempotent to the
set of nilpotents in the set of $n\times n$ matrices in terms of
the norm of the idempotent. We construct explicit idempotents and
nilpotents which achieve these distances, and determine exact
distances in some special cases.
Keywords:operator, matrix, nilpotent, idempotent, projection Categories:47A15, 47D03, 15A30 
29. CJM 2007 (vol 59 pp. 276)
Weighted Inequalities for HardySteklov Operators We characterize the pairs of weights $(v,w)$ for which the
operator $Tf(x)=g(x)\int_{s(x)}^{h(x)}f$ with $s$ and $h$
increasing and continuous functions is of strong type
$(p,q)$ or weak type $(p,q)$ with respect to the pair
$(v,w)$ in the case $0

30. CJM 2007 (vol 59 pp. 311)
Growth and Zeros of the Zeta Function for Hyperbolic Rational Maps This paper describes new results on the growth and zeros of the Ruelle
zeta function for the Julia set of a hyperbolic rational map. It is
shown that the zeta function is bounded by $\exp(C_K s^{\delta})$ in
strips $\Real s \leq K$, where $\delta$ is the dimension of the
Julia set. This leads to bounds on the number of zeros in strips
(interpreted as the PollicottRuelle resonances of this dynamical
system). An upper bound on the number of zeros in polynomial regions
$\{\Real s  \leq \Imag s^\alpha\}$ is given, followed by weaker
lower bound estimates in strips $\{\Real s > C, \Imag s\leq r\}$,
and logarithmic neighbourhoods
$\{ \Real s  \leq \rho \log \Imag s \}$.
Recent numerical work of StrainZworski suggests the upper
bounds in strips are optimal.
Keywords:zeta function, transfer operator, complex dynamics Category:37C30 
31. CJM 2005 (vol 57 pp. 897)
Representation of Banach Ideal Spaces and Factorization of Operators Representation theorems are proved for Banach ideal spaces with the Fatou property
which are built by the Calder{\'o}nLozanovski\u\i\ construction.
Factorization theorems for operators in spaces more general than the Lebesgue
$L^{p}$ spaces are investigated. It is natural to extend the Gagliardo
theorem on the Schur test and the Rubio de~Francia theorem on factorization of the
Muckenhoupt $A_{p}$ weights to reflexive Orlicz spaces. However, it turns out that for
the scales far from $L^{p}$spaces this is impossible. For the concrete integral operators
it is shown that factorization theorems and the Schur test in some reflexive Orlicz spaces
are not valid. Representation theorems for the Calder{\'o}nLozanovski\u\i\ construction
are involved in the proofs.
Keywords:Banach ideal spaces, weighted spaces, weight functions,, CalderÃ³nLozanovski\u\i\ spaces, Orlicz spaces, representation of, spaces, uniqueness problem, positive linear operators, positive sublinear, operators, Schur test, factorization of operators, f Categories:46E30, 46B42, 46B70 
32. CJM 2005 (vol 57 pp. 598)
Local Solvability of Laplacian Difference Operators Arising from the Discrete Heisenberg Group Differential operators $D_x$, $D_y$, and $D_z$ are formed using the
action of the $3$dimensional discrete Heisenberg group $G$ on a set
$S$, and the operators will act on functions on $S$. The Laplacian
operator $L=D_x^2 + D_y^2 + D_z^2$ is a difference operator with
variable differences which can be associated to a unitary
representation of $G$ on the Hilbert space $L^2(S)$. Using techniques
from harmonic analysis and representation theory, we show that the
Laplacian operator is locally solvable.
Keywords:discrete Heisenberg group,, unitary representation,, local solvability,, difference operator Categories:43A85, 22D10, 39A70 
33. CJM 2005 (vol 57 pp. 61)
On Operators with Spectral Square but without Resolvent Points Decompositions of spectral type are
obtained for closed Hilbert space operators with empty resolvent
set, but whose square has closure which is spectral. Krein space
situations are also discussed.
Keywords:unbounded operators, closed operators,, spectral resolution, indefinite metric Categories:47A05, 47A15, 47B40, 47B50, 46C20 
34. CJM 2003 (vol 55 pp. 1264)
Admissible Majorants for Model Subspaces of $H^2$, Part II: Fast Winding of the Generating Inner Function 
Admissible Majorants for Model Subspaces of $H^2$, Part II: Fast Winding of the Generating Inner Function This paper is a continuation of \cite{HM02I}. We consider the model
subspaces $K_\Theta=H^2\ominus\Theta H^2$ of the Hardy space $H^2$
generated by an inner function $\Theta$ in the upper half plane. Our
main object is the class of admissible majorants for $K_\Theta$,
denoted by $\Adm \Theta$ and consisting of all functions $\omega$
defined on $\mathbb{R}$ such that there exists an $f \ne 0$, $f \in
K_\Theta$ satisfying $f(x)\leq\omega(x)$ almost everywhere on
$\mathbb{R}$. Firstly, using some simple Hilbert transform techniques,
we obtain a general multiplier theorem applicable to any $K_\Theta$
generated by a meromorphic inner function. In contrast with
\cite{HM02I}, we consider the generating functions $\Theta$ such that
the unit vector $\Theta(x)$ winds up fast as $x$ grows from $\infty$
to $\infty$. In particular, we consider $\Theta=B$ where $B$ is a
Blaschke product with ``horizontal'' zeros, {\it i.e.}, almost
uniformly distributed in a strip parallel to and separated from $\mathbb{R}$.
It is shown, among other things, that for any such $B$, any even
$\omega$ decreasing on $(0,\infty)$ with a finite logarithmic integral
is in $\Adm B$ (unlike the ``vertical'' case treated in \cite{HM02I}),
thus generalizing (with a new proof) a classical result related to
$\Adm\exp(i\sigma z)$, $\sigma>0$. Some oscillating $\omega$'s in
$\Adm B$ are also described. Our theme is related to the
BeurlingMalliavin multiplier theorem devoted to $\Adm\exp(i\sigma z)$,
$\sigma>0$, and to de~Branges' space $\mathcal{H}(E)$.
Keywords:Hardy space, inner function, shift operator, model, subspace, Hilbert transform, admissible majorant Categories:30D55, 47A15 
35. CJM 2003 (vol 55 pp. 1231)
Admissible Majorants for Model Subspaces of $H^2$, Part I: Slow Winding of the Generating Inner Function 
Admissible Majorants for Model Subspaces of $H^2$, Part I: Slow Winding of the Generating Inner Function A model subspace $K_\Theta$ of the Hardy space $H^2 = H^2
(\mathbb{C}_+)$ for the upper half plane $\mathbb{C}_+$ is
$H^2(\mathbb{C}_+) \ominus \Theta H^2(\mathbb{C}_+)$ where $\Theta$
is an inner function in $\mathbb{C}_+$. A function $\omega \colon
\mathbb{R}\mapsto[0,\infty)$ is called {\it an admissible
majorant\/} for $K_\Theta$ if there exists an $f \in K_\Theta$, $f
\not\equiv 0$, $f(x)\leq \omega(x)$ almost everywhere on
$\mathbb{R}$. For some (mainly meromorphic) $\Theta$'s some parts
of $\Adm\Theta$ (the set of all admissible majorants for
$K_\Theta$) are explicitly described. These descriptions depend on
the rate of growth of $\arg \Theta$ along $\mathbb{R}$. This paper
is about slowly growing arguments (slower than $x$). Our results
exhibit the dependence of $\Adm B$ on the geometry of the zeros of
the Blaschke product $B$. A complete description of $\Adm B$ is
obtained for $B$'s with purely imaginary (``vertical'') zeros. We
show that in this case a unique minimal admissible majorant exists.
Keywords:Hardy space, inner function, shift operator, model, subspace, Hilbert transform, admissible majorant Categories:30D55, 47A15 
36. CJM 2002 (vol 54 pp. 1280)
Besov Spaces and Hausdorff Dimension For Some CarnotCarathÃ©odory Metric Spaces We regard a system of left invariant vector fields $\mathcal{X}=\{X_1,\dots,X_k\}$
satisfying the H\"ormander condition and the related CarnotCarath\'eodory metric on a
unimodular Lie group $G$. We define Besov spaces corresponding to the subLaplacian
$\Delta=\sum X_i^2$ both with positive and negative smoothness. The atomic
decomposition of the spaces is given. In consequence we get the distributional
characterization of the Hausdorff dimension of Borel subsets with the Haar measure
zero.
Keywords:Besov spaces, subelliptic operators, CarnotCarathÃ©odory metric, Hausdorff dimension Categories:46E35, 43A15, 28A78 
37. CJM 2002 (vol 54 pp. 1121)
Fully Nonlinear Elliptic Equations on General Domains By means of the Pucci operator, we construct a function $u_0$, which plays
an essential role in our considerations, and give the existence and regularity
theorems for the bounded viscosity solutions of the generalized Dirichlet
problems of second order fully nonlinear elliptic equations on the general
bounded domains, which may be irregular. The approximation method, the accretive
operator technique and the Caffarelli's perturbation theory are used.
Keywords:Pucci operator, viscosity solution, existence, $C^{2,\psi}$ regularity, Dini condition, fully nonlinear equation, general domain, accretive operator, approximation lemma Categories:35D05, 35D10, 35J60, 35J67 
38. CJM 2002 (vol 54 pp. 916)
ConvexitÃ©, complÃ¨te monotonie et inÃ©galitÃ©s sur les fonctions zÃªta et gamma sur les fonctions des opÃ©rateurs de Baskakov et sur des fonctions arithmÃ©tiques 
ConvexitÃ©, complÃ¨te monotonie et inÃ©galitÃ©s sur les fonctions zÃªta et gamma sur les fonctions des opÃ©rateurs de Baskakov et sur des fonctions arithmÃ©tiques We give optimal upper and lower bounds for the function
$H(x,s)=\sum_{n\geq 1}\frac{1}{(x+n)^s}$ for $x\geq 0$ and $s>1$. These
bounds improve the standard inequalities with integrals. We deduce from them
inequalities about Riemann's $\zeta$ function, and we give a conjecture
about the monotonicity of the function
$s\mapsto[(s1)\zeta(s)]^{\frac{1}{s1}}$. Some applications concern the
convexity of functions related to Euler's $\Gamma$ function and optimal
majorization of elementary functions of Baskakov's operators. Then, the
result proved for the function $x\mapsto x^{s}$ is extended to completely
monotonic functions. This leads to easy evaluation of the order of the
generating series of some arithmetical functions when $z$ tends to 1. The
last part is concerned with the class of non negative decreasing convex
functions on $]0,+\infty[$, integrable at infinity.
Nous prouvons un encadrement optimal pour la quantit\'e
$H(x,s)=\sum_{n\geq 1}\frac{1}{(x+n)^s}$ pour $x\geq 0$ et $s>1$, qui
am\'eliore l'encadrement standard par des int\'egrales. Cet encadrement
entra{\^\i}ne des in\'egalit\'es sur la fonction $\zeta$ de Riemann, et
am\`ene \`a conjecturer la monotonie de la fonction
$s\mapsto[(s1)\zeta(s)]^{\frac{1}{s1}}$. On donne des applications \`a
l'\'etude de la convexit\'e de fonctions li\'ees \`a la fonction $\Gamma$
d'Euler et \`a la majoration optimale des fonctions \'el\'ementaires
intervenant dans les op\'erateurs de Baskakov. Puis, nous \'etendons aux
fonctions compl\`etement monotones sur $]0,+\infty[$ les r\'esultats \'etablis
pour la fonction $x\mapsto x^{s}$, et nous en d\'eduisons des preuves
\'el\'ementaires du comportement, quand $z$ tend vers $1$, des s\'eries
g\'en\'eratrices de certaines fonctions arithm\'etiques. Enfin, nous
prouvons qu'une partie du r\'esultat se g\'en\'eralise \`a une classe de
fonctions convexes positives d\'ecroissantes.
Keywords:arithmetical functions, Baskakov's operators, completely monotonic functions, convex functions, inequalities, gamma function, zeta function Categories:26A51, 26D15 
39. CJM 2002 (vol 54 pp. 1100)
The Operator Biprojectivity of the Fourier Algebra In this paper, we investigate projectivity in the category of operator
spaces. In particular, we show that the Fourier algebra of a locally
compact group $G$ is operator biprojective if and only if $G$ is
discrete.
Keywords:locally compact group, Fourier algebra, operator space, projective Categories:13D03, 18G25, 43A95, 46L07, 22D99 
40. CJM 2002 (vol 54 pp. 945)
Approximation on Closed Sets by Analytic or Meromorphic Solutions of Elliptic Equations and Applications 
Approximation on Closed Sets by Analytic or Meromorphic Solutions of Elliptic Equations and Applications Given a homogeneous elliptic partial differential operator $L$ with constant
complex coefficients and a class of functions (jetdistributions) which
are defined on a (relatively) closed subset of a domain $\Omega$ in $\mathbf{R}^n$ and
which belong locally to a Banach space $V$, we consider the problem of
approximating in the norm of $V$ the functions in this class by ``analytic''
and ``meromorphic'' solutions of the equation $Lu=0$. We establish new Roth,
Arakelyan (including tangential) and Carleman type theorems for a large class
of Banach spaces $V$ and operators $L$. Important applications to boundary
value problems of solutions of homogeneous elliptic partial differential
equations are obtained, including the solution of a generalized Dirichlet
problem.
Keywords:approximation on closed sets, elliptic operator, strongly elliptic operator, $L$meromorphic and $L$analytic functions, localization operator, Banach space of distributions, Dirichlet problem Categories:30D40, 30E10, 31B35, 35Jxx, 35J67, 41A30 
41. CJM 2001 (vol 53 pp. 565)
Spaces of Lorentz Multipliers We study when the spaces of Lorentz multipliers from $L^{p,t}
\rightarrow L^{p,s}$ are distinct. Our main interest is the case when
$s Keywords:multipliers, convolution operators, Lorentz spaces, Lorentzimproving multipliers Categories:43A22, 42A45, 46E30 
42. CJM 2000 (vol 52 pp. 381)
Hardy Space Estimate for the Product of Singular Integrals $H^p$ estimate for the multilinear operators which are finite sums
of pointwise products of singular integrals and fractional
integrals is given. An application to Sobolev space and some
examples are also given.
Keywords:$H^p$ space, multilinear operator, singular integral, fractional integration, Sobolev space Category:42B20 
43. CJM 1998 (vol 50 pp. 193)
Intertwining operator and $h$harmonics associated with reflection groups We study the intertwining operator and $h$harmonics in
Dunkl's theory on $h$harmonics associated with reflection groups. Based
on a biorthogonality between the ordinary harmonics and the action of the
intertwining operator $V$ on the harmonics, the main result provides a
method to compute the action of the intertwining operator $V$ on polynomials
and to construct an orthonormal basis for the space of $h$harmonics.
Keywords:$h$harmonics, intertwining operator, reflection group Categories:33C50, 33C45 