1,341 research outputs found
Future challenges in cephalopod research
We thank Anto´nio M. de Frias Martins, past President of the Unitas Malacologica and Peter Marko, President of the American Malacological Society for organizing the 2013 World Congress of Malacology, and the Cephalopod International Advisory Committee for endorsing a symposium held in honour of Malcolm R. Clarke. In particular, we would like to thank the many professional staff from the University of the Azores for their hospitality, organization, troubleshooting and warm welcome to the Azores. We also thank Malcolm Clarke’s widow, Dorothy, his daughter Zoe¨, Jose´ N. Gomes-Pereira and numerous colleagues and friends of Malcolm’s from around the world for joining us at Ponta Delgada. We are grateful to Lyndsey Claro (Princeton University Press) for granting copyright permissions.Peer reviewedPublisher PD
Convexity in partial cubes: the hull number
We prove that the combinatorial optimization problem of determining the hull
number of a partial cube is NP-complete. This makes partial cubes the minimal
graph class for which NP-completeness of this problem is known and improves
some earlier results in the literature.
On the other hand we provide a polynomial-time algorithm to determine the
hull number of planar partial cube quadrangulations.
Instances of the hull number problem for partial cubes described include
poset dimension and hitting sets for interiors of curves in the plane.
To obtain the above results, we investigate convexity in partial cubes and
characterize these graphs in terms of their lattice of convex subgraphs,
improving a theorem of Handa. Furthermore we provide a topological
representation theorem for planar partial cubes, generalizing a result of
Fukuda and Handa about rank three oriented matroids.Comment: 19 pages, 4 figure
Discovery of two M32 twins in Abell 1689
The M31 satellite galaxy M32 has long been considered an object of unique
properties, being the most extreme example of the very rare compact elliptical
galaxy class. Here we present the spectroscopic discovery of two M32 twins in
the massive galaxy cluster Abell 1689. As these objects are so rare, this is an
important step towards a better understanding of the nature of compact
galaxies. The two M32 twins had first been detected within our photometric
search for ultra compact dwarf galaxy (UCDs) candidates in A1689 (Mieske et al.
2004) with the Advanced Camera for Surveys (ACS). Their luminosities (M_V ~ -17
mag) are very similar to M32 and their surface brightness profiles are
consistent with that of M32 projected to A1689's distance. From our ACS imaging
we detect several fainter compact galaxy candidates with luminosities
intermediate between M32 and the Fornax UCDs. If spectroscopically confirmed as
cluster members, this would almost close the gap in the magnitude-surface
brightness plane between the region of UCDs and the compact ellipticals,
implying a sequence of faint compact galaxies well separated from that of dwarf
ellipticals.Comment: 5 pages, 5 figures, accepted for publication in A&A letter
A simple radionuclide-driven single-ion source
We describe a source capable of producing single barium ions through nuclear
recoils in radioactive decay. The source is fabricated by electroplating 148Gd
onto a silicon {\alpha}-particle detector and vapor depositing a layer of BaF2
over it. 144Sm recoils from the alpha decay of 148Gd are used to dislodge Ba+
ions from the BaF2 layer and emit them in the surrounding environment. The
simultaneous detection of an {\alpha} particle in the substrate detector allows
for tagging of the nuclear decay and of the Ba+ emission. The source is simple,
durable, and can be manipulated and used in different environments. We discuss
the fabrication process, which can be easily adapted to emit most other
chemical species, and the performance of the source
Development and optimization of a new suspension system for lower limb prosthesis
The increasing rate of lower limb amputations reinforces the need to develop a new suspension system that provides a better quality of life for the lower limb amputees. This study aimed to present a novel suspension system that improves amputee’s satisfaction in terms of donning and doffing process of the prosthetic lower limb. The design of the proposed suspension system was developed following the design methodology, to establish the amputee’s needs, objectives, functions, requirements and specifications in order to op-timize the final solution. The final solution is a combination of a guiding and fixation mechanisms that improve the donning and doffing process by driv-ing the serrated pin to the fixation system. The proposed suspension system is a good alternative to improve the quality of life of amputees with lower activity level on the daily basis.(undefined
Vitamins A, C and E and the risk of breast cancer: results from a case-control study in Greece
Although several dietary compounds are hypothesized to have anticarcinogenic properties, the role ofpecific micronutrients in the development of breast cancer remains unclear. To address this issue, we assessed intake of retinol,
β-carotene, vitamin C and vitamin E in relation to breast cancer risk in a case–control study in Greece. Eight hundrednd twenty women with histologically confirmed breast cancer were compared with 1548 control women. Dietary data were collectedhrough a 115-item semiquantitative food frequency questionnaire. Data were modelled by logistic regression, with adjustment forotal energy intake and established breast cancer risk factors, as well as mutual adjustment among the micronutrients. Amongost-menopausal women, there was no association between any of the micronutrients evaluated and risk of breast cancer. Amongremenopausal women, β-carotene, vitamin C and vitamin E were each inversely associated with breast cancer risk, but afterutual adjustment among the three nutrients only β-carotene remained significant; the odds ratio (OR) for a one-quintilencrease in β-carotene intake was 0.84 (95% confidence interval 0.73–0.97). The inverse association observed with
β-carotene intake, however, is slightly weaker than the association previously observed with vegetable intake in these data,aising the possibility that the observed β-carotene effect is accounted for by another component of vegetables. ©1999 Cancer Research Campaig
Bars in early- and late-type disks in COSMOS
We investigate the (large-scale) bar fraction in a mass-complete sample of M
> 10^10.5 Msun disk galaxies at 0.2 < z < 0.6 in the COSMOS field. The fraction
of barred disks strongly depends on mass, disk morphology, and specific star
formation rate (SSFR). At intermediate stellar mass (10^10.5 < M < 10^11 Msun)
the bar fraction in early-type disks is much higher, at all redshifts, by a
factor ~2, than that in late-type disks. This trend is reversed at higher
stellar mass (M > 10^11 Msun), where the fraction of bars in early-type disks
becomes significantly lower, at all redshifts, than that in late-type disks.
The bar fractions for galaxies with low and high SSFRs closely follow those of
the morphologically-selected early-type and late-type populations,
respectively. This indicates a close correspondence between morphology and SSFR
in disk galaxies at these earlier epochs. Interestingly, the total bar fraction
in 10^10.5 < M < 10^11 Msun disks is built up by a factor of ~2 over the
redshift interval explored, while for M > 10^11 Msun disks it remains roughly
constant. This indicates that, already by z ~ 0.6, spectral and morphological
transformations in the most massive disk galaxies have largely converged to the
familiar Hubble sequence that we observe in the local Universe, while for
intermediate mass disks this convergence is ongoing until at least z ~ 0.2.
Moreover, these results highlight the importance of employing mass-limited
samples for quantifying the evolution of barred galaxies. Finally, the
evolution of the barred galaxy populations investigated does not depend on the
large-scale environmental density (at least, on the scales which can be probed
with the available photometric redshifts).Comment: 10 pages, 4 figures, updated to reflect version accepted by MNRA
Search for nucleon decays with EXO-200
A search for instability of nucleons bound in Xe nuclei is reported
with 223 kgyr exposure of Xe in the EXO-200 experiment. Lifetime
limits of 3.3 and 1.9 yrs are established for
nucleon decay to Sb and Te, respectively. These are the most
stringent to date, exceeding the prior decay limits by a factor of 9 and 7,
respectively
A critical review of the evidence for M32 being a compact dwarf satellite of M31 rather than a more distant normal galaxy
Since Baade's photographic study of M32 in the mid 1940s, it has been
accepted as an established fact that M32 is a compact dwarf satellite of M31.
The purpose of this paper is to report on the findings of our investigation
into the nature of the existing evidence. We find that the case for M32 being a
satellite of M31 rests upon Hubble Space Telescope (HST) based stellar
population studies which have resolved red-giant branch (RGB) and red clump
stars in M32 as well as other nearby galaxies. Taken in isolation, this recent
evidence could be considered to be conclusive in favour of the existing view.
However, the conventional scenario does not explain M32's anomalously high
central velocity dispersion for a dwarf galaxy (several times that of either
NGC 147, NGC 185 or NGC 205) or existing planetary nebula observations (which
suggest that M32 is more than twice as distant as M31) and also requires an
elaborate physical explanation for M32's inferred compactness. Conversely, we
find that the case for M32 being a normal galaxy, of the order of three times
as distant as M31, is supported by: (1) a central velocity dispersion typical
of intermediate galaxies, (2) the published planetary nebula observations, and
(3) known scaling relationships for normal early-type galaxies. However, this
novel scenario cannot account for the high apparent luminosities of the RGB
stars resolved in the M32 direction by HST observations. We are therefore left
with two apparently irreconcilable scenarios, only one of which can be correct,
but both of which suffer from potentially fatal evidence to the contrary. This
suggests that current understanding of some relevant fields is still very far
from adequate.Comment: 17 pages, 3 Postscript figures, uses cjaa.cls and natbib.sty
(published version has 16 pages
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