105,843 research outputs found
The Complex X-ray Spectrum of the Sefyert 1.5 Source NGC 6860
The X-ray spectrum of the Seyfert 1.5 source NGC 6860 is among the most
complex of the sources detected in the Swift Burst Alert Telescope all-sky
survey. A short XMM-Newton follow-up observation of the source revealed a flat
spectrum both above and below 2 keV. To uncover the complexity of the source,
in this paper we analyze both a 40 ks Suzaku and a 100 ks XMM-Newton
observation of NGC 6860. While the spectral state of the source changed between
the newer observations presented here and the earlier short XMM-Newton spectrum
- showing a higher flux and steeper power law component - the spectrum of NGC
6860 is still complex with clearly detected warm absorption signatures. We find
that a two component warm ionized absorber is present in the soft spectrum,
with column densities of about 10^20 and 10^21 cm$^-2, ionization parameters of
xi = 180 and 45 ergs cm s^-1, and outflow velocities for each component in the
range of 0-300 km s^-1. Additionally, in the hard spectrum we find a broad
(approx 11000 km s^-1) Fe K-alpha emission line, redshifted by approx 2800 km
s^-1.Comment: 35 pages, 9 figures, Accepted to Ap
The nuclear dimension of C*-algebras
We introduce the nuclear dimension of a C*-algebra; this is a noncommutative
version of topological covering dimension based on a modification of the
earlier concept of decomposition rank. Our notion behaves well with respect to
inductive limits, tensor products, hereditary subalgebras (hence ideals),
quotients, and even extensions. It can be computed for many examples; in
particular, it is finite for all UCT Kirchberg algebras. In fact, all classes
of nuclear C*-algebras which have so far been successfully classified consist
of examples with finite nuclear dimension, and it turns out that finite nuclear
dimension implies many properties relevant for the classification program.
Surprisingly, the concept is also linked to coarse geometry, since for a
discrete metric space of bounded geometry the nuclear dimension of the
associated uniform Roe algebra is dominated by the asymptotic dimension of the
underlying space.Comment: 33 page
Geographical issues and physics applications of "very" long neutrino factory baselines
We discuss several potential applications of ``very'' long neutrino factory
baselines, as well as potential detector locations for these applications.Comment: 2 pages, 2 figures; Talk given at the NuFact 05 workshop, June 21-26,
Frascati, Ital
Lavrentiev Phenomenon in Microstructure Theory
A variational problem arising as a model in martensitic phase transformation
including surface energy is studied. It explains the complex,
multi-dimensional pattern of twin branching which is often observed in a
martensitic phase near the austenite interface.
We prove that a Lavrentiev phenomenon can occur
if the domain is a rectangle. We show that this phenomenon
disappears under arbitrarily small shears
of the domain. We also prove that other perturbations of the problem lead to
an extinction of the Lavrentiev phenomenon
Simple C*-algebras with locally finite decomposition rank
We introduce the notion of locally finite decomposition rank, a structural
property shared by many stably finite nuclear C*-algebras. The concept is
particularly relevant for Elliott's program to classify nuclear C*-algebras by
K-theory data. We study some of its properties and show that a simple unital
C*-algebra, which has locally finite decomposition rank, real rank zero and
which absorbs the Jiang-Su algebra Z tensorially, has tracial rank zero in the
sense of Lin. As a consequence, any such C*-algebra, if it additionally
satisfies the Universal Coefficients Theorem, is approximately homogeneous of
topological dimension at most 3. Our result in particular confirms the Elliott
conjecture for the class of simple unital Z-stable ASH algebras with real rank
zero. Moreover, it implies that simple unital Z-stable AH algebras with real
rank zero not only have slow dimension growth in the ASH sense, but even in the
AH sense.Comment: 30 pages, no figure
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