200,027 research outputs found
Inverse Classification for Comparison-based Interpretability in Machine Learning
In the context of post-hoc interpretability, this paper addresses the task of
explaining the prediction of a classifier, considering the case where no
information is available, neither on the classifier itself, nor on the
processed data (neither the training nor the test data). It proposes an
instance-based approach whose principle consists in determining the minimal
changes needed to alter a prediction: given a data point whose classification
must be explained, the proposed method consists in identifying a close
neighbour classified differently, where the closeness definition integrates a
sparsity constraint. This principle is implemented using observation generation
in the Growing Spheres algorithm. Experimental results on two datasets
illustrate the relevance of the proposed approach that can be used to gain
knowledge about the classifier.Comment: preprin
3D Integral Field Observations of Ten Galactic Winds - I. Extended phase (>10 Myr) of mass/energy injection before the wind blows
We present 3D spectroscopic observations of a sample of 10 nearby galaxies
with the AAOmega-SPIRAL integral field spectrograph on the 3.9m AAT, the
largest survey of its kind to date. The double-beam spectrograph provides
spatial maps in a range of spectral diagnostics: [OIII] 5007, H-beta, Mg-b,
NaD, [OI] 6300, H-alpha, [NII] 6583, [SII] 6717, 6731. All of the objects in
our survey show extensive wind-driven filamentation along the minor axis, in
addition to large-scale disk rotation. Our sample can be divided into either
starburst galaxies or active galactic nuclei (AGN), although some objects
appear to be a combination of these. The total ionizing photon budget available
to both classes of galaxies is sufficient to ionise all of the wind-blown
filamentation out to large radius. We find however that while AGN
photoionisation always dominates in the wind filaments, this is not the case in
starburst galaxies where shock ionisation dominates. This clearly indicates
that after the onset of star formation, there is a substantial delay (> 10 Myr)
before a starburst wind develops. We show why this behavior is expected by
deriving ``ionisation'' and dynamical timescales for both AGNs and starbursts.
We establish a sequence of events that lead to the onset of a galactic wind.
The clear signature provided by the ionisation timescale is arguably the
strongest evidence yet that the starburst phenomenon is an impulsive event. A
well-defined ionisation timescale is not expected in galaxies with a protracted
history of circumnuclear star formation. Our 3D data provide important
templates for comparisons with high redshift galaxies.[Abridged]Comment: 43 pages, 30 figures, Accepted for publication in ApJ Jan-2010, Full
resolution figures available from:
http://www.aao.gov.au/AAO/local/www/rgs/work/winds/public/papers/SPIRAL_WINDS_hi-res.htm
The FUV to Near-IR Morphologies of Luminous Infrared Galaxies in the GOALS Sample
We compare the morphologies of a sample of 20 LIRGs from the Great
Observatories All-sky LIRG Survey (GOALS) in the FUV, B, I and H bands, using
the Gini (G) and M20 parameters to quantitatively estimate the distribution and
concentration of flux as a function of wavelength. HST images provide an
average spatial resolution of ~80 pc. While our LIRGs can be reliably
classified as mergers across the entire range of wavelengths studied here,
there is a clear shift toward more negative M20 (more bulge-dominated) and a
less significant decrease in G values at longer wavelengths. We find no
correlation between the derived FUV G-M20 parameters and the global measures of
the IR to FUV flux ratio, IRX. Given the fine resolution in our HST data, this
suggests either that the UV morphology and IRX are correlated on very small
scales, or that the regions emitting the bulk of the IR emission emit almost no
FUV light. We use our multi-wavelength data to simulate how merging LIRGs would
appear from z~0.5-3 in deep optical and near-infrared images such as the HUDF,
and use these simulations to measure the G-M20 at these redshifts. Our
simulations indicate a noticeable decrease in G, which flattens at z >= 2 by as
much as 40%, resulting in mis-classifying our LIRGs as disk-like, even in the
rest-frame FUV. The higher redshift values of M20 for the GOALS sources do not
appear to change more than about 10% from the values at z~0. The change in
G-M20 is caused by the surface brightness dimming of extended tidal features
and asymmetries, and also the decreased spatial resolution which reduced the
number of individual clumps identified. This effect, seen as early as z~0.5,
could easily lead to an underestimate of the number of merging galaxies at
high-redshift in the rest-frame FUV.Comment: Accepted for publication in the Astronomical Journal. The total page
count is 15 pages with 13 figures and 1 Tabl
Simultaneous inference for misaligned multivariate functional data
We consider inference for misaligned multivariate functional data that
represents the same underlying curve, but where the functional samples have
systematic differences in shape. In this paper we introduce a new class of
generally applicable models where warping effects are modeled through nonlinear
transformation of latent Gaussian variables and systematic shape differences
are modeled by Gaussian processes. To model cross-covariance between sample
coordinates we introduce a class of low-dimensional cross-covariance structures
suitable for modeling multivariate functional data. We present a method for
doing maximum-likelihood estimation in the models and apply the method to three
data sets. The first data set is from a motion tracking system where the
spatial positions of a large number of body-markers are tracked in
three-dimensions over time. The second data set consists of height and weight
measurements for Danish boys. The third data set consists of three-dimensional
spatial hand paths from a controlled obstacle-avoidance experiment. We use the
developed method to estimate the cross-covariance structure, and use a
classification setup to demonstrate that the method outperforms
state-of-the-art methods for handling misaligned curve data.Comment: 44 pages in total including tables and figures. Additional 9 pages of
supplementary material and reference
Wolf-Rayet stars probed by AMBER/VLTI
Massive stars deeply influence their surroundings by their luminosity and the
injection of kinetic energy. So far, they have mostly been studied with
spatially unresolved observations, although evidence of geometrical complexity
of their wind are numerous. Interferometry can provide spatially resolved
observations of massive stars and their immediate vicinity. Specific geometries
(disks, jets, latitude-dependent winds) can be probed by this technique. The
first observation of a Wolf-Rayet (WR) star (\gamma^2 Vel) with the AMBER/VLTI
instrument yielded to a re-evaluation of its distance and an improved
characterization of the stellar components, from a very limited data-set. This
motivated our team to increase the number of WR targets observed with AMBER. We
present here new preliminary results that encompass several spectral types,
ranging from early WN to evolved dusty WC. We present unpublished data on
WR79a, a massive star probably at the boundary between the O and Wolf- Rayet
type, evidencing some Wolf-Rayet broad emission lines from an optically thin
wind. We also present new data obtained on \gamma^2 Vel that can be compared to
the up-to-date interferometry-based orbital parameters from North et al.
(2007). We discuss the presence of a wind-wind collision zone in the system and
provide preliminary analysis suggesting the presence of such a structure in the
data. Then, we present data obtained on 2 dusty Wolf-Rayet stars: WR48a-b and
WR118, the latter exhibiting some clues of a pinwheel-like structure from the
visibility variations.Comment: This paper will be published in the proceeding of SPIE ``astronomical
Telescopes and Instrumentation: Optical and Infrared Interferometry'
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