6,197 research outputs found
Causal Fermion Systems: A Quantum Space-Time Emerging from an Action Principle
Causal fermion systems are introduced as a general mathematical framework for
formulating relativistic quantum theory. By specializing, we recover earlier
notions like fermion systems in discrete space-time, the fermionic projector
and causal variational principles. We review how an effect of spontaneous
structure formation gives rise to a topology and a causal structure in
space-time. Moreover, we outline how to construct a spin connection and
curvature, leading to a proposal for a "quantum geometry" in the Lorentzian
setting. We review recent numerical and analytical results on the support of
minimizers of causal variational principles which reveal a "quantization
effect" resulting in a discreteness of space-time. A brief survey is given on
the correspondence to quantum field theory and gauge theories.Comment: 23 pages, LaTeX, 2 figures, footnote added on page
Parameter estimation in pair hidden Markov models
This paper deals with parameter estimation in pair hidden Markov models
(pair-HMMs). We first provide a rigorous formalism for these models and discuss
possible definitions of likelihoods. The model being biologically motivated,
some restrictions with respect to the full parameter space naturally occur.
Existence of two different Information divergence rates is established and
divergence property (namely positivity at values different from the true one)
is shown under additional assumptions. This yields consistency for the
parameter in parametrization schemes for which the divergence property holds.
Simulations illustrate different cases which are not covered by our results.Comment: corrected typo
Stormy weather in 3C 196.1: nuclear outbursts and merger events shape the environment of the hybrid radio galaxy 3C 196.1
We present a multi-wavelength analysis based on archival radio, optical and
X-ray data of the complex radio source 3C 196.1, whose host is the brightest
cluster galaxy of a cluster. HST data show H+[N II] emission
aligned with the jet 8.4 GHz radio emission. An H+[N II] filament
coincides with the brightest X-ray emission, the northern hotspot. Analysis of
the X-ray and radio images reveals cavities located at galactic- and cluster-
scales. The galactic-scale cavity is almost devoid of 8.4 GHz radio emission
and the south-western H+[N II] emission is bounded (in projection) by
this cavity. The outer cavity is co-spatial with the peak of 147 MHz radio
emission, and hence we interpret this depression in X-ray surface brightness as
being caused by a buoyantly rising bubble originating from an AGN outburst
280 Myrs ago. A \textit{Chandra} snapshot observation allowed us to
constrain the physical parameters of the cluster, which has a cool core with a
low central temperature 2.8 keV, low central entropy index 13 keV
cm and a short cooling time of 500 Myr, which is of the age
of the Universe at this redshift. By fitting jumps in the X-ray density we
found Mach numbers between 1.4 and 1.6, consistent with a shock origin. We also
found compelling evidence of a past merger, indicated by a morphology
reminiscent of gas sloshing in the X-ray residual image. Finally, we computed
the pressures, enthalpies and jet powers associated with
the cavities: erg,
erg s for the inner cavity and erg,
erg s for the outer cavity.Comment: 14 pages, 4 figures, ApJ accepte
Infrared Diagnostics for the Extended 12 micron Sample of Seyferts
We present an analysis of Spitzer IRS spectroscopy of 83 active galaxies from
the extended 12 micron sample. We find rank correlations between several
tracers of star formation which suggest that (1) the PAH feature is a reliable
tracer of star formation, (2) there is a significant contribution to the
heating of the cool dust by stars, (3) the H emission is also primarily
excited by star formation. The 55-90 vs. 20-30 spectral index plot is also a
diagnostic of the relative contribution of Starburst to AGN. We see there is a
large change in spectral index across the sample. Thus, the contribution to the
IR spectrum from the AGN and starburst components can be comparable in
magnitude but the relative contribution also varies widely across the sample.
We find rank correlations between several AGN tracers. We search for
correlations between AGN and Starburst tracers and we conclude that the AGN and
Starburst tracers are not correlated. This is consistent with our conclusion
that the relative strength of the AGN and Starburst components varies widely
across the sample. Thus, there is no simple link between AGN fueling and Black
Hole Growth and star formation in these galaxies. The distribution of Sil 10
micron and 18 micron strengths is consistent with the clumpy torus models of
Sirocky et al. We find a rank correlation between the [NeV] 14 micron line and
the 6.7 micron continuum which may be due to an extended component of hot dust.
The Sy 2s with a Hidden Broad Line Region (HBLR) have a higher ratio of AGN to
Starburst contribution to the SED than Sy 2s without an HBLR. This may
contribute to the detection of the HBLR in polarized light. The Sy 2s with an
HBLR are more similar to the Sy 1s than they are to the Sy 2s without an HBLR
Inducing Probabilistic Grammars by Bayesian Model Merging
We describe a framework for inducing probabilistic grammars from corpora of
positive samples. First, samples are {\em incorporated} by adding ad-hoc rules
to a working grammar; subsequently, elements of the model (such as states or
nonterminals) are {\em merged} to achieve generalization and a more compact
representation. The choice of what to merge and when to stop is governed by the
Bayesian posterior probability of the grammar given the data, which formalizes
a trade-off between a close fit to the data and a default preference for
simpler models (`Occam's Razor'). The general scheme is illustrated using three
types of probabilistic grammars: Hidden Markov models, class-based -grams,
and stochastic context-free grammars.Comment: To appear in Grammatical Inference and Applications, Second
International Colloquium on Grammatical Inference; Springer Verlag, 1994. 13
page
Rigidity of compact Riemannian spin Manifolds with Boundary
In this article, we prove new rigidity results for compact Riemannian spin
manifolds with boundary whose scalar curvature is bounded from below by a
non-positive constant. In particular, we obtain generalizations of a result of
Hang-Wang \cite{hangwang1} based on a conjecture of Schroeder and Strake
\cite{schroeder}.Comment: English version of "G\'eom\'etrie spinorielle extrins\`eque et
rigidit\'es", Corollary 6 in Section 3 added, to appear in Letters Math. Phy
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