2,439 research outputs found
Slicing Sets and Measures, and the Dimension of Exceptional Parameters
We consider the problem of slicing a compact metric space \Omega with sets of
the form \pi_{\lambda}^{-1}\{t\}, where the mappings \pi_{\lambda} \colon
\Omega \to \R, \lambda \in \R, are \emph{generalized projections}, introduced
by Yuval Peres and Wilhelm Schlag in 2000. The basic question is: assuming that
\Omega has Hausdorff dimension strictly greater than one, what is the dimension
of the 'typical' slice \pi_{\lambda}^{-1}{t}, as the parameters \lambda and t
vary. In the special case of the mappings \pi_{\lambda} being orthogonal
projections restricted to a compact set \Omega \subset \R^{2}, the problem
dates back to a 1954 paper by Marstrand: he proved that for almost every
\lambda there exist positively many such that \dim
\pi_{\lambda}^{-1}{t} = \dim \Omega - 1. For generalized projections, the same
result was obtained 50 years later by J\"arvenp\"a\"a, J\"arvenp\"a\"a and
Niemel\"a. In this paper, we improve the previously existing estimates by
replacing the phrase 'almost all \lambda' with a sharp bound for the dimension
of the exceptional parameters.Comment: 31 pages, three figures; several typos corrected and large parts of
the third section rewritten in v3; to appear in J. Geom. Ana
Super star clusters and Supernovae in interacting LIRGs unmasked by NIR adaptive optics
We report on an on-going near-IR adaptive optics survey targeting interacting
luminous IR galaxies. High-spatial resolution NIR data are crucial to enable
interpretation of kinematic, dynamical and star formation (SF) properties of
these very dusty objects. Whole progenitor nuclei in the interactions can be
missed if only optical HST imaging is used. Here we specifically present the
latest results regarding core-collapse supernovae found within the highly
extincted nuclear regions of these galaxies. Direct detection and study of such
highly obscured CCSNe is crucial for revising the optically-derived SN rates
used for providing an independent measurement of the SF history of the
Universe. We also present thus-far the first NIR luminosity functions of super
star cluster (SSC) candidates. The LFs can then be used to constrain the
formation and evolution of SSCs via constraints based on initial mass functions
and cluster disruption models.Comment: 6 pages. To appear in proceedings of 'Galaxies and their Masks'
(Namibia, April 2010), published by Springer, New York, eds. D.L. Block, K.C.
Freeman, I. Puerar
How large dimension guarantees a given angle?
We study the following two problems:
(1) Given and \al, how large Hausdorff dimension can a compact set
A\su\Rn have if does not contain three points that form an angle \al?
(2) Given \al and \de, how large Hausdorff dimension can a %compact
subset of a Euclidean space have if does not contain three points that
form an angle in the \de-neighborhood of \al?
An interesting phenomenon is that different angles show different behaviour
in the above problems. Apart from the clearly special extreme angles 0 and
, the angles and also play special
role in problem (2): the maximal dimension is smaller for these special angles
than for the other angles. In problem (1) the angle seems to behave
differently from other angles
Higher-dimensional multifractal value sets for conformal infinite graph directed Markov systems
We give a description of the level sets in the higher dimensional
multifractal formalism for infinite conformal graph directed Markov systems. If
these systems possess a certain degree of regularity this description is
complete in the sense that we identify all values with non-empty level sets and
determine their Hausdorff dimension. This result is also partially new for the
finite alphabet case.Comment: 20 pages, 1 figur
Sixty Years of Fractal Projections
Sixty years ago, John Marstrand published a paper which, among other things,
relates the Hausdorff dimension of a plane set to the dimensions of its
orthogonal projections onto lines. For many years, the paper attracted very
little attention. However, over the past 30 years, Marstrand's projection
theorems have become the prototype for many results in fractal geometry with
numerous variants and applications and they continue to motivate leading
research.Comment: Submitted to proceedings of Fractals and Stochastics
Metal-ligand interplay in strongly-correlated oxides: a parametrized phase diagram for pressure induced spin transitions
We investigate the magnetic properties of archetypal transition-metal oxides
MnO, FeO, CoO and NiO under very high pressure by x-ray emission spectroscopy
at the K\beta line. We observe a strong modification of the magnetism in the
megabar range in all the samples except NiO. The results are analyzed within a
multiplet approach including charge-transfer effects. The pressure dependence
of the emission line is well accounted for by changes of the ligand field
acting on the d electrons and allows us to extract parameters like local
d-hybridization strength, O-2p bandwidth and ionic crystal field across the
magnetic transition. This approach allows a first-hand insight into the
mechanism of the pressure induced spin transition.Comment: 5 pages, 3 figure
Temperature and pressure-induced spin-state transitions in LaCoO3
We report the continuous variation of the spin moment of cobalt in LaCoO3
across its temperature and pressure-induced spin transitions evidenced with
K\beta emission spectra. The first thermal transition is best described by a
transition to an orbitally nondegenerate intermediate spin (S=1) state. In
parallel, continuous redistribution of the 3d electrons is also indicated by
partial fluorescence yield X-ray absorption spectra. At high pressure, our
study confirms that the material becomes low spin between 40 and 70 kbar at
room temperature
Supernovae and radio transients in M 82
We present optical and near-infrared (IR) photometry and near-IR spectroscopy
of SN 2004am, the only optically detected supernova (SN) in M 82. These
demonstrate that SN 2004am was a highly reddened type II-P SN similar to the
low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN
2004am was located coincident with the obscured super star cluster M 82-L, and
from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to
this, we present a high spatial resolution Gemini-N K-band adaptive optics
image of the site of SN 2008iz and a second transient of uncertain nature, both
detected so far only at radio wavelengths. Using image subtraction techniques
together with archival data from the Hubble Space Telescope, we are able to
recover a near-IR transient source co-incident with both objects. We find the
likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of
the second transient remains elusive and we regard an extremely bright
microquasar in M 82 as the most plausible scenario.Comment: 14 pages, 8 figures, accepted for publication in MNRA
- …