3,394 research outputs found
On excesses of frames
We show that any two frames in a separable Hilbert space that are dual to
each other have the same excess. Some new relations for the analysis resp.
synthesis operators of dual frames are also derived. We then prove that
pseudo-dual frames and, in particular, approximately dual frames have the same
excess. We also discuss various results on frames in which excesses of frames
play an important role.Comment: 12 page
Oblique projections and frames
We characterize those frames on a Hilbert space H which can be represented as the image of an orthonormal basis by an oblique projection defined on an extension K of H. We show that all frames with infinite excess, and frame bounds 1 ≤ A ≤ B,are of this type. This gives a generalization of a result of Han and Larson which only holds for normalized tight frames.Fil: Antezana, Jorge Abel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Argentino de Matemática Alberto Calderón; ArgentinaFil: Corach, Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Argentino de Matemática Alberto Calderón; ArgentinaFil: Ruiz, Mariano Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Argentino de Matemática Alberto Calderón; ArgentinaFil: Stojanoff, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Argentino de Matemática Alberto Calderón; Argentin
The Schur-Horn theorem for operators and frames with prescribed norms and frame operator
Let be a Hilbert space. Given a bounded positive definite
operator on , and a bounded sequence of non negative real numbers, the pair is
frame admissible, if there exists a frame on
with frame operator , such that , . We relate the existence of such frames with the Schur-Horn
theorem of majorization, and give a reformulation of the extended version of
Schur-Horn theorem, due to A. Neumann. We use it to get necessary conditions
(and to generalize known sufficient conditions) for a pair ,
to be frame admissible.Comment: To appear in Illinois Journal of Mat
Identification of Faint Chandra X-ray Sources in the Core-Collapsed Globular Cluster NGC 6752
We have searched for optical identifications for 39 Chandra X-ray sources
that lie within the 1.9 arcmin half-mass radius of the nearby (d = 4.0 kpc),
core-collapsed globular cluster, NGC 6752, using deep Hubble Space Telescope
ACS/WFC imaging in B435, R625, and H alpha. Photometry of these images allows
us to classify candidate counterparts based primarily on color-magnitude and
color-color diagram location. The color-color diagram is particularly useful
for quantifying the H alpha line equivalent width. In addition to recovering 11
previously detected optical counterparts, we propose 20 new optical IDs. In
total, there are 16 likely or less certain cataclysmic variables (CVs), nine
likely or less certain chromospherically active binaries, three galaxies, and
three active galactic nuclei (AGNs). The latter three sources, which had been
identified as likely CVs by previous investigations, now appear to be
extragalactic objects based on their proper motions. As we previously found for
NGC 6397, the CV candidates in NGC 6752 fall into a bright group that is
centrally concentrated relative to the turnoff-mass stars and a faint group
that has a spatial distribution that is more similar to that of the
turnoff-mass stars. This is consistent with an evolutionary scenario in which
CVs are produced by dynamical interactions near the cluster center and diffuse
to larger radius orbits as they age.Comment: 26 pages, 18 figure
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