1,874 research outputs found
An HI survey of the Centaurus and Sculptor Groups - Constraints on the space density of low mass galaxies
We present results of two 21-cm HI surveys performed with the Australia
Telescope Compact Array in the nearby Centaurus A and Sculptor galaxy groups.
These surveys are sensitive to compact HI clouds and galaxies with HI masses as
low as 3E+06 Msun, and are therefore among the most sensitive extragalactic HI
surveys to date. The surveys consist of sparsely spaced pointings that sample
approximately 2% of the groups' area on the sky. We detected previously known
group members, but we found no new HI clouds or galaxies down to the
sensitivity limit of the surveys. If the HI mass function had a faint end slope
of alpha = 1.5 below M_{HI} = 10^{7.5} Msun in these groups, we would have
expected ~3 new objects. Cold dark matter theories of galaxy formation predict
the existence of a large number low mass DM sub-halos that might appear as tiny
satellites in galaxy groups. Our results support and extend similar conclusions
derived from previous HI surveys that a HI rich population of these satellites
does not exist.Comment: Accepted for publication in A&
A taxonomy of sublinear multiple keyword pattern matching algorithms
AbstractThis article presents a taxonomy of sublinear keyword pattern matching algorithms related to the Boyer-Moore algorithm [3] and the Commentz-Walter algorithm [5, 6]. The taxonomy includes, amongst others, the multiple keyword generalization of the single keyword Boyer-Moore algorithm and an algorithm by Fan and Su [9, 10]. The corresponding precomputation algorithms are presented as well. The taxonomy is based on the idea of ordering algorithms according to their essential problem and algorithm details, and deriving all algorithms from a common starting point by successively adding these details in a correctness preserving way. This way of presentation not only provides a complete correctness argument of each algorithm, but also makes very clear what algorithms have in common (the details of their nearest common ancestor) and where they differ (the details added after their nearest common ancestor). Introduction of the notion of safe shift distances proves to be essential in the derivation and classification of the algorithms. Moreover, the article provides a common derivation for and a uniform presentation of the precomputation algorithms, not yet found in the literature
Impacts of CO2-taxes in an economy with niche markets and learning-by-doing.
[Dataset available: http://hdl.handle.net/10411/16384]
The curious case of J113924.74+164144.0: a possible new group of galaxies at z = 0.0693
J113924.74+164144.0 is an interesting galaxy at z = 0.0693, i.e. D_L ~ 305
Mpc, with tidal-tail-like extended optical features on both sides. There are
two neighbouring galaxies, a spiral galaxy J113922.85+164136.3 which has a
strikingly similar 'tidal' morphology, and a faint galaxy J113923.58+164129.9.
We report HI 21 cm observations of this field to search for signatures of
possible interaction. Narrow HI emission is detected from J113924.74+164144.0,
but J113922.85+164136.3 shows no detectable emission. The total HI mass
detected in J113924.74+164144.0 is 7.7 x 10^9 M_solar. The HI emission from the
galaxy is found to be extended and significantly offset from the optical
position of the galaxy. We interpret this as signature of possible interaction
with the neighbouring spiral galaxy. There is also a possible detection of HI
emission from another nearby galaxy J113952.31+164531.8 at z = 0.0680 at a
projected distance of 600 kpc, and with a total HI mass of 5.3 x 10^9 M_solar,
suggesting that all these galaxies form a loose group at z ~ 0.069.Comment: 5 pages, 1 table, 6 figures. Accepted for publication in MNRAS
Letters. The definitive version will be available at
http://www.blackwell-synergy.com
The link between Somalian Plate rotation and the East African Rift System: an analogue modelling study
The East African Rift System (EARS) represents a major
tectonic feature that splits the African continent between the Nubian Plate
situated to the west and the Somalian Plate to the east. The EARS comprises
various rift segments and microplates and represents a key location for
studying rift evolution. Researchers have proposed various scenarios for the
evolution of the EARS, but the impact of continent-scale rotational rifting,
linked to the rotation of the Somalian Plate, has received only limited
attention. In this study we apply analogue models to explore the dynamic
evolution of the EARS within its broader rotational-rifting framework. Our
models show that rotational rifting leads to the lateral propagation of
deformation towards the rotation axis, which reflects the general southward
propagation of the EARS. However, we must distinguish between the
propagation of distributed deformation, which can move very rapidly, and
localized deformation, which can significantly lag behind the former. The
various structural-weakness arrangements in our models (simulating the
pre-existing lithospheric heterogeneities that localize rifting along the
EARS) lead to a variety of structures. Laterally overlapping weaknesses are
required for localizing parallel rift basins to create rift pass structures,
leading to the rotation and segregation of microplates such as the Victoria
Plate in the EARS, as well as to the simultaneous north- and southward
propagation of the adjacent Western Rift. Additional model observations
concern the development of early pairs of rift-bounding faults flanking the
rift basins, followed by the localization of deformation along the axes of
the most developed rift basins. Furthermore, the orientation of rift
segments with respect to the regional (rotational) plate divergence affects
deformation along these segments: oblique rift segments are less wide due to
a strike-slip deformation component. Overall, our model results generally
fit the large-scale present-day features of the EARS, with implications for
general rift development and for the segregation and rotation of the
Victoria Plate.</p
Exploring the causes of adverse events in hospitals and potential prevention strategies
Objectives
To examine the causes of adverse events
(AEs) and potential prevention strategies to minimise the
occurrence of AEs in hospitalised patients.
Methods
For the 744 AEs identified in the patient record
review study in 21 Dutch hospitals, trained reviewers
were asked to select all causal factors that contributed
to the AE. The results were analysed together with data
on preventability and consequences of AEs. In addition,
the reviewers selected one or more prevention strategies
for each preventable AE. The recommended prevention
strategies were analysed together with four general
causal categories: technical, human, organisational and
patient-related factors.
Results
Human causes were predominantly involved in
the causation of AEs (in 61% of the AEs), 61% of those
being preventable and 13% leading to permanent
disability. In 39% of the AEs, patient-related factors were
involved, in 14% organisational factors and in 4%
technical factors. Organisational causes contributed
relatively often to preventable AEs (93%) and AEs
resulting in permanent disability (20%). Recommended
strategies to prevent AEs were quality assurance/peer
review, evaluation of safety behaviour, training and
procedures. For the AEs with human and patient-related
causes, reviewers predominantly recommended quality
assurance/peer review. AEs caused by organisational
factors were considered preventable by improving
procedures.
Discussion
Healthcare interventions directed at human
causes are recommended because these play a large
role in AE causation. In addition, it seems worthwhile to
direct interventions on organisational causes because the
AEs they cause are nearly always believed to be
preventable. Organisational factors are thus relatively
easy to tackle. Future research designs should allow
researchers to interview healthcare providers that were
involved in the event, as an additional source of
information on contributing factors.
The Arecibo Legacy Fast ALFA Survey: VIII. HI Source Catalog of the Anti-Virgo Region at dec = +25 deg
We present a fourth catalog of HI sources from the Arecibo Legacy Fast ALFA
(ALFALFA) Survey. We report 541 detections over 136 deg2, within the region of
the sky having 22h < R.A. < 03h and 24 deg < Dec. < 26 deg . This complements a
previous catalog in the region 26 deg < Dec. < 28 deg (Saintonge et al. 2008).
We present here the detections falling into three classes: (a) extragalactic
sources with S/N > 6.5, where the reliability of the catalog is better than
95%; (b) extragalactic sources 5.0 < S/N < 6.5 and a previously measured
optical redshift that corroborates our detection; or (c) High Velocity Clouds
(HVCs), or subcomponents of such clouds, in the periphery of the Milky Way. Of
the 541 objects presented here, 90 are associated with High Velocity Clouds,
while the remaining 451 are identified as extragalactic objects. Optical
counterparts have been matched with all but one of the extragalactic objects.Comment: 26 pages, 5 figures, 1 table, accepted for publication in
Astrophysical Journal Supplement Serie
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