664 research outputs found
Improving Generalization for Abstract Reasoning Tasks Using Disentangled Feature Representations
In this work we explore the generalization characteristics of unsupervised
representation learning by leveraging disentangled VAE's to learn a useful
latent space on a set of relational reasoning problems derived from Raven
Progressive Matrices. We show that the latent representations, learned by
unsupervised training using the right objective function, significantly
outperform the same architectures trained with purely supervised learning,
especially when it comes to generalization
Detection of a relic X-ray jet in Cygnus A
We present a 200 ks Chandra ACIS-I image of Cygnus A, and discuss a long
linear feature seen in its counterlobe. This feature has a non-thermal spectrum
and lies on the line connecting the brighter hotspot on the approaching side
and the nucleus. We therefore conclude that this feature is (or was) a jet.
However, the outer part of this X-ray jet does not trace the current counterjet
observed in radio. No X-ray counterpart is observed on the jet side. Using
light-travel time effects we conclude that this X-ray 50 kpc linear feature is
a relic jet that contains enough low-energy plasma (gamma ~ 10^3) to
inverse-Compton scatter cosmic microwave background photons, producing emission
in the X-rays.Comment: 4 pages. Proceedings of "High Energy Phenomena in Relativistic
Outflows", held in Dublin, Ireland, September 24-28, 200
Multiwavelength study of Cygnus A IV. Proper motion and location of the nucleus
Context. Cygnus A, as the nearest powerful FR II radio galaxy, plays an
important role in understanding jets and their impact on the surrounding
intracluster medium. Aims. To explain why the nucleus is observed superposed
onto the eastern lobe rather than in between the two lobes, and why the jet and
counterjet are non-colinear. Methods. We made a comparative study of the radio
images at different frequencies of Cygnus A, in combination with the published
results on the radial velocities in the Cygnus A cluster. Results. From the
morphology of the inner lobes we conclude that the lobes are not interacting
with one another, but are well separated, even at low radio frequencies. We
explain the location of the nucleus as the result of the proper motion of the
galaxy through the cluster. The required proper motion is of the same order of
magnitude as the radial velocity offset of Cygnus A with the sub-cluster it
belongs to. The proper motion of the galaxy through the cluster likely also
explains the non-co-linearity of the jet and counterjet.Comment: Accepted for publication in A&A, 8 pages, 4 figure
Long-term outcome of meniscus and cruciate ligament stabilization in the injured knee.
De lange termijn resultaten van meniscale suturen en voorste kruisband reconstructies worden geëvalueerd. Meniscale suturen in stabiele knieën geven de beste resultaten. De kans op het ontwikkelen van vroegtijdige degeneratieve veranderingen (arthrose) is 4 maal hoger bij meniscus herstel in instabiele knieën (vorste kruisband deficient) tov. meniscus herstel in stabierle knieën
Preservice elementary school teachers' knowledge of fractions: a mirror of students' knowledge?
This research analyses preservice teachers' knowledge of fractions. Fractions are notoriously difficult for students to learn and for teachers to teach. Previous studies suggest that student learning of fractions may be limited by teacher understanding of fractions. If so, teacher education has a key role in solving the problem. We first reviewed literature regarding students' knowledge of fractions. We did so because assessments of required content knowledge for teaching require review of the students' understanding to determine the mathematics difficulties encountered by students. The preservice teachers were tested on their conceptual and procedural knowledge of fractions, and on their ability in explaining the rationale for a procedure or the conceptual meaning. The results revealed that preservice teachers' knowledge of fractions indeed is limited and that last-year preservice teachers did not perform better than first-year preservice teachers. This research is situated within the broader domain of mathematical knowledge for teaching and suggests ways to improve instruction and student learning
Curriculum sequencing and the acquisition of clock reading skills among Chinese and Flemish children
The present study reexamines the adoption of clock reading skills in the primary mathematics curriculum. In many Western countries, the mathematics curriculum adopts a number of age-related stages for teaching clock reading skills, that were defined by early research (e.g., Friedman & laycock, 1989; Piaget, 1969). Through a comparison of Flemish and Chinese student’s clock reading abilities, the current study examines whether these age-related stages are a solid base for teaching clock reading skills. By means of both quantitative (ANOVA’s) and qualitative (textbook analysis) methods, the present study indicates that the alternative way of teaching clock reading skills in China, i.e., at the age of six instead of staggered out over several grades, results in a two years earlier acquisition of clock reading skills. This indicates that the previously age-related stages in children’s acquisition of clock reading are not universal, nor the most effective way to teach these skills to young children
Variability of the coronal line region in NGC 4151
We present the first extensive study of the coronal line variability in an
active galaxy. Our data set for the nearby source NGC 4151 consists of six
epochs of quasi-simultaneous optical and near-infrared spectroscopy spanning a
period of about eight years and five epochs of X-ray spectroscopy overlapping
in time with it. None of the coronal lines showed the variability behaviour
observed for the broad emission lines and hot dust emission. In general, the
coronal lines varied only weakly, if at all. Using the optical [Fe VII] and
X-ray O VII emission lines we estimate that the coronal line gas has a
relatively low density of n~10^3 cm^-3 and a relatively high ionisation
parameter of log U~1. The resultant distance of the coronal line gas from the
ionising source is about two light years, which puts this region well beyond
the hot inner face of the obscuring dusty torus. The high ionisation parameter
implies that the coronal line region is an independent entity rather than part
of a continuous gas distribution connecting the broad and narrow emission line
regions. We present tentative evidence for the X-ray heated wind scenario of
Pier & Voit. We find that the increased ionising radiation that heats the dusty
torus also increases the cooling efficiency of the coronal line gas, most
likely due to a stronger adiabatic expansion.Comment: 12 pages, 9 figures; accepted by MNRA
Multiwavelength study of Cygnus A III. Evidence for relic lobe plasma
We study the particle energy distribution in the cocoon surrounding Cygnus A,
using radio images between 151 MHz and 15 GHz and a 200 ks Chandra ACIS-I
image. We show that the excess low frequency emission in the the lobe further
from Earth cannot be explained by absorption or excess adiabatic expansion of
the lobe or a combination of both. We show that this excess emission is
consistent with emission from a relic counterlobe and a relic counterjet that
are being re-energized by compression from the current lobe. We detect hints of
a relic hotspot at the end of the relic X-ray jet in the more distant lobe. We
do not detect relic emission in the lobe nearer to Earth as expected from light
travel-time effects assuming intrinsic symmetry. We determine that the duration
of the previous jet activity phase was slightly less than that of the current
jet-active phase. Further, we explain some features observed at 5 and 15 GHz as
due to the presence of a relic jet.Comment: Accepted for publication with MNRAS, 10 pages with 10 figure
Strong variability of the coronal line region in NGC 5548
We present the second extensive study of the coronal line variability in an
active galaxy. Our data set for the well-studied Seyfert galaxy NGC 5548
consists of five epochs of quasi-simultaneous optical and near-infrared
spectroscopy spanning a period of about five years and three epochs of X-ray
spectroscopy overlapping in time with it. Whereas the broad emission lines and
hot dust emission varied only moderately, the coronal lines varied strongly.
However, the observed high variability is mainly due to a flux decrease. Using
the optical [FeVII] and X-ray OVII emission lines we estimate that the coronal
line gas has a relatively low density of n~10^3/cm^3 and a relatively high
ionisation parameter of log U~1. The resultant distance of the coronal line gas
from the ionising source of about eight light years places this region well
beyond the hot inner face of the dusty torus. These results imply that the
coronal line region is an independent entity. We find again support for the
X-ray heated wind scenario of Pier & Voit; the increased ionising radiation
that heats the dusty torus also increases the cooling efficiency of the coronal
line gas, most likely due to a stronger adiabatic expansion. The much stronger
coronal line variability of NGC 5548 relative to that of NGC 4151 can also be
explained within this picture. NGC 5548 has much stronger coronal lines
relative to the low ionisation lines than NGC 4151 indicating a stronger wind,
in which case a stronger adiabatic expansion of the gas and so fading of the
line emission is expected.Comment: 10 pages, 6 figures; accepted for publication in MNRAS. arXiv admin
note: substantial text overlap with arXiv:1501.0292
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