265 research outputs found
Making Legacy LMS adaptable using Policy and Policy templates
Koesling, A., Herder, E., De Coi, J., & Abel, F. (2008). Making Legacy LMS adaptable using Policy and Policy templates. In J. Baumeister & M. Atzmüller, Proceedings of the 16th Workshop on Adaptivity and User Modeling in Interactive System, ABIS 2008 (pp. 35-40). October, 6-8, 2008, Würzburg, Germany: University of Würzburg.
Website with link to proceedings: http://lwa08.informatik.uni-wuerzburg.de/Wiki.jsp?page=FGABIS08In this paper, we discuss how users and designers
of existing learning management systems
(LMSs) can make use of policies to enhance
adaptivity and adaptability. Many widespread
LMSs currently only use limited and proprietary
rule systems defining the system behaviour. Personalization
of those systems is done based on
those rule systems allowing only for fairly restricted
adaptation rules. Policies allow for more
sophisticated and flexible adaptation rules, provided
by multiple stakeholders and they can be
integrated into legacy systems. We present the
benefits and feasibility of our ongoing approach
of extending an existing LMS with policies. We
will use the LMS ILIAS as a hands-on example
to allow users to make use of system personalization.The work on this publication has been sponsored by the TENCompetence Integrated Project that is funded by the European Commission's 6th Framework Programme, priority IST/Technology Enhanced Learning. Contract 027087 [http://www.tencompetence.org
Preference Search Service - Specification and Implementation
While the growing number of learning resources increases the
choice for learners, it also makes it more and more difficult to
find suitable courses. Thus, improved search capabilities on
learning resource repositories are required.
In this document, we describe the implementation of our
approach for learning resource search based on preference
queries. The implementation comprises a Web Service as well
as a java package supporting the client development for the
service. This Web Service acts as one part of the
TENCompetence Personalization Services developed in WP7.The work on this publication has been sponsored by the TENCompetence Integrated Project that is funded by the European Commission's 6th Framework Programme, priority IST/Technology Enhanced Learning. Contract 027087 [http://www.tencompetence.org
Male mate choice scales female ornament allometry in a cichlid fish
<p>Abstract</p> <p>Background</p> <p>Studies addressing the adaptive significance of female ornamentation have gained ground recently. However, the expression of female ornaments in relation to body size, known as trait allometry, still remains unexplored. Here, we investigated the allometry of a conspicuous female ornament in <it>Pelvicachromis taeniatus</it>, a biparental cichlid that shows mutual mate choice and ornamentation. Females feature an eye-catching pelvic fin greatly differing from that of males.</p> <p>Results</p> <p>We show that allometry of the female pelvic fin is scaled more positively in comparison to other fins. The pelvic fin exhibits isometry, whereas the other fins (except the caudal fin) show negative allometry. The size of the pelvic fin might be exaggerated by male choice because males prefer female stimuli that show a larger extension of the trait. Female pelvic fin size is correlated with individual condition, suggesting that males can assess direct and indirect benefits.</p> <p>Conclusions</p> <p>The absence of positive ornament allometry might be a result of sexual selection constricted by natural selection: fins are related to locomotion and thus may be subject to viability selection. Our study provides evidence that male mate choice might scale the expression of a female sexual ornament, and therefore has implications for the understanding of the relationship of female sexual traits with body size in species with conventional sex-roles.</p
The narrow-line quasar NAB 0205+024 observed with XMM-Newton
The XMM-Newton observation of the narrow-line quasar NAB 0205+024 reveals
three striking differences since it was last observed in the X-rays with ASCA.
Firstly, the 2-10 keV power-law is notably steeper. Secondly, a hard X-ray
flare is detected, very similar to that seen in I Zw 1. Thirdly, a strong and
broad emission feature is detected with the bulk of its emission redward of 6.4
keV, and extending down to ~5 keV in the rest frame. The most likely
explanation for the broad feature is neutral iron emission emitted from a
narrow annulus of an accretion disc close to the black hole. The hard X-ray
flare could be the mechanism which illuminates this region of the disc,
allowing for the emission line to be detected. The combination of effects can
be understood in terms of the `thundercloud' model proposed by Merloni &
Fabian.Comment: 7 pages. Accepted for publication in MNRA
High resolution soft X-ray spectroscopy of the elliptical galaxy NGC 5044. Results from the reflection grating spectrometer on-board XMM-Newton
The results from an X-ray spectroscopic study of the giant elliptical galaxy
NGC5044 in the center of a galaxy group are presented. The line dominated soft
X-ray spectra (mainly Fe-L and O VIII Ly_a) from the diffuse gas are resolved
for the first time in this system with the Reflection Grating Spectrometers
on-board XMM-Newton and provide a strong constraint on the temperature
structure. The spectra integrated over 2' (\sim 20kpc) in full-width can be
described by a two temperature plasma model of 0.7keV and 1.1keV. Most of the
latter component is consistent with originating from off-center regions.
Compared to the isobaric cooling flow prediction, the observation shows a clear
cut-off below a temperature of 0.6 +-0.1keV. Furthermore, the Fe and O
abundances within the central 10--20kpc in radius are accurately measured to be
0.55+-0.05 and 0.25+-0.1 times the solar ratios, respectively. The observed
cut-off temperature of this galaxy and other central galaxies in galaxy groups
and clusters are compared with the scale of the galaxy and properties of the
surrounding intra-cluster medium. Based on this comparison, the origin of the
lack of predicted cool emission is discussed.Comment: Accepted for publication in Astronomy & Astrophysic
Cold fronts and multi-temperature structures in the core of Abell 2052
The physics of the coolest phases in the hot Intra-Cluster Medium (ICM) of
clusters of galaxies is yet to be fully unveiled. X-ray cavities blown by the
central Active Galactic Nucleus (AGN) contain enough energy to heat the
surrounding gas and stop cooling, but locally blobs or filaments of gas appear
to be able to cool to low temperatures of 10^4 K. In X-rays, however, gas with
temperatures lower than 0.5 keV is not observed. Using a deep XMM-Newton
observation of the cluster of galaxies Abell 2052, we derive 2D maps of the
temperature, entropy, and iron abundance in the core region. About 130 kpc
South-West of the central galaxy, we discover a discontinuity in the surface
brightness of the hot gas which is consistent with a cold front. Interestingly,
the iron abundance jumps from ~0.75 to ~0.5 across the front. In a smaller
region to the North-West of the central galaxy we find a relatively high
contribution of cool 0.5 keV gas, but no X-ray emitting gas is detected below
that temperature. However, the region appears to be associated with much cooler
H-alpha filaments in the optical waveband. The elliptical shape of the cold
front in the SW of the cluster suggests that the front is caused by sloshing of
the hot gas in the clusters gravitational potential. This effect is probably an
important mechanism to transport metals from the core region to the outer parts
of the cluster. The smooth temperature profile across the sharp jump in the
metalicity indicates the presence of heat conduction and the lack of mixing
across the discontinuity. The cool blob of gas NW of the central galaxy was
probably pushed away from the core and squeezed by the adjacent bubble, where
it can cool efficiently and relatively undisturbed by the AGN. Shock induced
mixing between the two phases may cause the 0.5 keV gas to cool non-radiatively
and explain our non-detection of gas below 0.5 keV.Comment: 11 pages, 9 figures, A&A, in pres
Light-induced photoisomerization of a diarylethene molecular switch on solidsurfaces
Diarylethenes are molecular switches, the state of which can efficiently be
controlled by illumination with ultraviolet or visible light. To use the
change in the molecular properties when switching between the two states for a
specific function, direct contact with solid surfaces is advantageous as it
provides immobilization. Here we present a study of a diarylethene derivate
(T-DAE, 1,2-bis(5-methyl-2-phenylthiazol-4-yl)cyclopent-1-ene) in direct
contact with highly ordered graphite as well as with semimetallic Bi(1 1 1)
surfaces by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy
and simulated spectra based on density functional theory. On both surfaces,
the molecule can be switched from its open to its closed form by 325–475 nm
broadband or ultraviolet illumination. On the other hand, back isomerization
to the ring-open T-DAE was not possible
The quasar PG 0844+349 in an X-ray weak state
In March 2009 the well-studied quasar, PG 0844+349, was discovered with Swift
to be in an X-ray weak state. A follow-up XMM-Newton observation several weeks
later generated a good quality spectrum of the source, showing substantial
curvature and spectral hardening. In combination with archival data at two
previous epochs when the source was in a bright state, we examine the long-term
spectral and timing properties of PG 0844+349 spanning nearly ten years and a
factor of ten in brightness. Partial covering and blurred reflection models are
compared to the data at each flux state while attempting to maintain
consistency between the various epochs. In terms of the blurred reflection
model, PG 0844+349 is in a reflection dominated state during the 2009 X-ray
weak observations, which can be understood in terms of light bending. Moreover,
the light bending scenario can also account for the short-term (i.e. ~1000s)
spectral variability in the source. Other models cannot be decisively ruled
out, but we note distinguishing features of the models that can be explored for
in higher signal-to-noise data from current and future observatories.Comment: 11 pages. Accepted for publication in MNRA
A long, hard look at MCG-6-30-15 with XMM-Newton II: detailed EPIC analysis and modelling
The bright Seyfert 1 galaxy MCG-6-30-15 has provided some of the best
evidence to date for the existence of supermassive black holes in active
galactic nuclei. Observations with ASCA revealed an X-ray iron line profile
shaped by strong Doppler and gravitational effects. In this paper the shape of
the iron line, its variability characteristics and the robustness of this
spectral interpretation are examined using the long XMM-Newton observation
taken in 2001. A variety of spectral models, both including and excluding the
effects of strong gravity, are compared to the data in a uniform fashion. The
results strongly favour models in which the spectrum is shaped by emission from
a relativistic accretion disc. It is far more difficult to explain the 3-10 keV
spectrum using models dominated by absorption (either by warm or partially
covering cold matter), emission line blends, curved continua or additional
continuum components. These provide a substantially worse fit to the data and
fail to explain other observations (such as the simultaneous BeppoSAX
spectrum). This reaffirms the veracity of the relativistic `disc line'
interpretation. The short term variability in the shape of the energy spectrum
is investigated and explained in terms of a two-component emission model. Using
a combination of spectral variability analyses the spectrum is successfully
decomposed into a variable power-law component (PLC) and a reflection dominated
component (RDC). The former is highly variable while the latter is
approximately constant throughout the observation, leading to the well-known
spectral variability patterns. (Abridged)Comment: 25 pages. 24 figures. Accepted for publication in MNRA
X-ray variability of the Narrow Line Seyfert 1 Galaxy PKS 0558-504
We present results from several XMM-Newton observations of the radio loud
Narrow-line Seyfert 1 galaxy (NLS1) PKS 0558-504. We find evidence for strong
and persistent X-ray variability, both on short and long time-scales. On short
time scales of ~2 hours the source varies smoothly by 15-20%; long term
variations by a factor of >2 could not be resolved in the relatively short
exposures: we find the source mostly in a `low' state, in 2 out of the 11
observations in a `high state'. X-ray flares seem to be recurrent with a time
scale of ~24 ksec which, if interpreted as the Keplerian time scale in the
disc, would place the emission region just outside the last stable orbit. The
X-ray spectrum of PKS 0558-504 can be well fitted by two Comptonization
components, one at moderate temperatures of kT ~ 4.5 keV and optical depths of
\~ 2, the other at high temperatures kT > 50 keV and low optical depths < 1.0.
These parameters are, however, subject to large errors due to the inherent
degeneracy of the Comptonization models. Flux variations of the source are
caused by changes of the colder component only, the hot component with
parameters very similar to those of BLS1 galaxies, stays constant. All results
fit nicely the picture that NLS1 galaxies are lower mass objects, accreting
close to the Eddington rate emitting X-rays from a very active magnetically
powered accretion disc corona.Comment: 11 pages, 10 figures, accepted for publication in A&
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