4,563 research outputs found
Compact composition operators on the Dirichlet space and capacity of sets of contact points
In this paper, we prove that for every compact set of the unit disk of
logarithmic capacity 0, there exists a Schur function both in the disk algebra
and in the Dirichlet space such that the associated composition operator is in
all Schatten classes (of the Dirichlet space), and for which the set of points
whose image touches the unit circle is equal to this compact set. We show that
for every bounded composition operator on the Dirichlet space and for every
point of the unit circle, the logarithmic capacity of the set of point having
this point as image is 0. We show that every compact composition operator on
the Dirichlet space is compact on the gaussian Hardy-Orlicz space; in
particular, it is in every Schatten class on the usual Hilbertian Hardy space.
On the other hand, there exists a Schur function such that the associated
composition operator is compact on the gaussian Hardy-Orlicz space, but which
is not even bounded on the Dirichlet space. We prove that the Schatten classes
on the Dirichlet space can be separated by composition operators. Also, there
exists a Schur function such that the associated composition operator is
compact on the Dirichlet space, but in no Schatten class
Compact composition operators on Bergman-Orlicz spaces
We construct an analytic self-map of the unit disk and an Orlicz
function for which the composition operator of symbol is compact
on the Hardy-Orlicz space , but not compact on the Bergman-Orlicz space
. For that, we first prove a Carleson embedding theorem,
and then characterize the compactness of composition operators on
Bergman-Orlicz spaces, in terms of Carleson function (of order 2). We show that
this Carleson function is equivalent to the Nevanlinna counting function of
order 2.Comment: 32 page
Thin sets of integers in Harmonic analysis and p-stable random Fourier series
We investigate the behavior of some thin sets of integers defined through
random trigonometric polynomial when one replaces Gaussian or Rademacher
variables by p-stable ones, with 1 < p < 2. We show that in one case this
behavior is essentially the same as in the Gaussian case, whereas in another
case, this behavior is entirely different
The canonical injection of the Hardy-Orlicz space into the Bergman-Orlicz space
We study the canonical injection from the Hardy-Orlicz space into
the Bergman-Orlicz space .Comment: 21 page
Weak compactness and Orlicz spaces
We give new proofs that some Banach spaces have Pe{\l}czy\'nski's property
Some new properties of composition operators associated with lens maps
We give examples of results on composition operators connected with lens
maps. The first two concern the approximation numbers of those operators acting
on the usual Hardy space . The last ones are connected with Hardy-Orlicz
and Bergman-Orlicz spaces and , and provide a negative answer
to the question of knowing if all composition operators which are weakly
compact on a non-reflexive space are norm-compact.Comment: 21 page
Some revisited results about composition operators on Hardy spaces
We generalize, on one hand, some results known for composition operators on
Hardy spaces to the case of Hardy-Orlicz spaces : construction of a
"slow" Blaschke product giving a non-compact composition operator on ;
construction of a surjective symbol whose composition operator is compact on
and, moreover, is in all the Schatten classes , . On
the other hand, we revisit the classical case of composition operators on
, giving first a new, and simplier, characterization of closed range
composition operators, and then showing directly the equivalence of the two
characterizations of membership in the Schatten classes of Luecking and
Luecking and Zhu.Comment: 21 page
La modelización y simulación computacional como metodología de investigación social
il presente trabajo se propone brindar una introducción crítica y sistemática a la metodología de modelado y simulación computacional en ciencias sociales. El uso de métodos computacionales para simular procesos sociales se ha expandido con vigor en los últimos veinte años en las distintas disciplinas de las ciencias sociales; sin embargo, continúa siendo una metodología poco conocida y empleada por los investigadores sociales en América Latina. El objetivo de este trabajo es contribuir a la reflexión epistemológica, teórica y metodológica de la simulación computacional en ciencias sociales, atendiendo a la dimensión política que atraviesa toda praxis científica
Confinement of Spin and Charge in High-Temperature Superconductors
By exploiting the internal gauge-invariance intrinsic to a spin-charge
separated electron, we show that such degrees of freedom must be confined in
two-dimensional superconductors experiencing strong inter-electron repulsion.
We also demonstrate that incipient confinement in the normal state can prevent
chiral spin-fluctuations from destroying the cross-over between strange and
psuedo-gap regimes in under-doped high-temperature superconductors. Last, we
suggest that the negative Hall anomaly observed in these materials is connected
with this confinement effect.Comment: 12 pages, 1 postscript figure, to appear in PRB (RC), May 199
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