10,152 research outputs found
The Topological Theory of the Milnor Invariant
We study a topological Abelian gauge theory that generalizes the Abelian
Chern-Simons one, and that leads in a natural way to the Milnor's link
invariant when the classical action on-shell is calculated.Comment: 4 pages; corrected equatio
Excited State Specific Multi-Slater Jastrow Wave Functions
We combine recent advances in excited state variational principles, fast
multi-Slater Jastrow methods, and selective configuration interaction to create
multi-Slater Jastrow wave function approximations that are optimized for
individual excited states. In addition to the Jastrow variables and linear
expansion coefficients, this optimization includes state-specific orbital
relaxations in order to avoid the compromises necessary in state-averaged
approaches. We demonstrate that, when combined with variance matching to help
balance the quality of the approximation across different states, this approach
delivers accurate excitation energies even when using very modest multi-Slater
expansions. Intriguingly, this accuracy is maintained even when studying a
difficult chlorine-anion-to- charge transfer in which traditional
state-averaged multi-reference methods must contend with different states that
require drastically different orbital relaxations.Comment: 16 pages, 6 figures, 2 table
[C II] emission from galactic nuclei in the presence of X-rays
The luminosity of [C II] is used to probe the star formation rate in
galaxies, but the correlation breaks down in some active galactic nuclei
(AGNs). Models of the [C II] emission from galactic nuclei do not include the
influence of X-rays on the carbon ionization balance, which may be a factor in
reducing the [C II] luminosity. We calculate the [C II] luminosity in galactic
nuclei under the influence of bright sources of X-rays. We solve the balance
equation of the ionization states of carbon as a function of X-ray flux,
electron, atomic hydrogen, and molecular hydrogen density. These are input to
models of [CII] emission from the interstellar medium (ISM) in galactic nuclei.
We also solve the distribution of the ionization states of oxygen and nitrogen
in highly ionized regions. We find that the dense warm ionized medium (WIM) and
dense photon dominated regions (PDRs) dominate the [C II] emission when no
X-rays are present. The X-rays in galactic nuclei can affect strongly the C
abundance in the WIM converting some fraction to C and higher ionization
states and thus reducing its [C II] luminosity. For an X-ray luminosity >
10 erg/s the [C II] luminosity can be suppressed by a factor of a few,
and for very strong sources, >10 erg/s, such as found for many AGNs by
an order of magnitude. Comparison of the model with extragalactic sources shows
that the [C II] to far-infrared ratio declines for an X-ray luminosity
>10 erg/s, in reasonable agreement with our model.Comment: 16 pages and 14 figures, accepted for publication in A&
EM Algorithms for Weighted-Data Clustering with Application to Audio-Visual Scene Analysis
Data clustering has received a lot of attention and numerous methods,
algorithms and software packages are available. Among these techniques,
parametric finite-mixture models play a central role due to their interesting
mathematical properties and to the existence of maximum-likelihood estimators
based on expectation-maximization (EM). In this paper we propose a new mixture
model that associates a weight with each observed point. We introduce the
weighted-data Gaussian mixture and we derive two EM algorithms. The first one
considers a fixed weight for each observation. The second one treats each
weight as a random variable following a gamma distribution. We propose a model
selection method based on a minimum message length criterion, provide a weight
initialization strategy, and validate the proposed algorithms by comparing them
with several state of the art parametric and non-parametric clustering
techniques. We also demonstrate the effectiveness and robustness of the
proposed clustering technique in the presence of heterogeneous data, namely
audio-visual scene analysis.Comment: 14 pages, 4 figures, 4 table
- …