41,814 research outputs found
A Direct Distance to the LMC Cepheid HV 12198 from the Infrared Surface Brightness Technique
We report on a first application of the infrared surface brightness technique
on a Cepheid in the Large Magellanic Cloud, the variable HV 12198 in the young
globular cluster NGC 1866. From this one star, we determine a distance modulus
of 18.42 +- 0.10 (random and systematic uncertainty) to the cluster. When the
results on further member Cepheids in NGC 1866 become available, we expect to
derive the distance to the LMC with a +- 3-4 percent accuracy, including
systematic errors, from this technique.Comment: 4 pages, 4 figures, accepted in ApJ Letter
Tuning grid storage resources for LHC data analysis
Grid Storage Resource Management (SRM) and local file-system solutions are facing significant challenges to support efficient analysis of the data now being produced at the Large Hadron Collider (LHC). We compare the performance of different storage technologies at UK grid sites examining the effects of tuning and recent improvements in the I/O patterns of experiment software. Results are presented for both live production systems and technologies not currently in widespread use. Performance is studied using tests, including real LHC data analysis, which can be used to aid sites in deploying or optimising their storage configuration
Enhanced Stability of Superheavy Nuclei due to High-Spin Isomerism
Configuration-constrained calculations of potential-energy surfaces in
even-even superheavy nuclei reveal systematically the existence at low
excitation energies of multi-quasiparticle states with deformed axially
symmetric shapes and large angular momenta. These results indicate the
prevalence of long-lived, multi-quasiparticle isomers. In a quantal system, the
ground state is usually more stable than the excited states. In contrast, in
superheavy nuclei the multi-qausiparticle excitations decrease the probability
for both fission and decay, implying enhanced stability. Hence, the
systematic occurrence of multi-qausiparticle isomers may become crucial for
future production and study of even heavier nuclei. The energies of
multi-quasiparticle states and their decays are calculated and
compared to available data.Comment: 4 pages, 5 figures, accepted for publication in PR
Antiferromagnetism and hot spots in CeIn
Enormous mass enhancement at ''hot spots'' on the Fermi surface (FS) of
CeIn has been reported at strong magnetic field near its antiferromagnetic
(AFM) quantum critical point [T. Ebihara et al., Phys. Rev. Lett. 93, 246401
(2004)] and ascribed to anomalous spin fluctuations at these spots. The ''hot
spots'' lie at the positions on FS where in non-magnetic LaIn the narrow
necks are protruded. In paramagnetic phase CeIn has similar spectrum. We
show that in the presence of AFM ordering its FS undergoes a topological change
at the onset of AFM order that truncates the necks at the ''hot spots'' for one
of the branches. Applied field leads to the logarithmic divergence of the dHvA
effective mass when the electron trajectory passes near or through the neck
positions. This effect explains the observed dHvA mass enhancement at the ''hot
spots'' and leads to interesting predictions concerning the spin-dependence of
the effective electron mass. The (T,B)-phase diagram of CeIn, constructed
in terms of the Landau functional, is in agreement with experiment.Comment: 4 pages, 1 figur
Learning Content Selection Rules for Generating Object Descriptions in Dialogue
A fundamental requirement of any task-oriented dialogue system is the ability
to generate object descriptions that refer to objects in the task domain. The
subproblem of content selection for object descriptions in task-oriented
dialogue has been the focus of much previous work and a large number of models
have been proposed. In this paper, we use the annotated COCONUT corpus of
task-oriented design dialogues to develop feature sets based on Dale and
Reiters (1995) incremental model, Brennan and Clarks (1996) conceptual pact
model, and Jordans (2000b) intentional influences model, and use these feature
sets in a machine learning experiment to automatically learn a model of content
selection for object descriptions. Since Dale and Reiters model requires a
representation of discourse structure, the corpus annotations are used to
derive a representation based on Grosz and Sidners (1986) theory of the
intentional structure of discourse, as well as two very simple representations
of discourse structure based purely on recency. We then apply the
rule-induction program RIPPER to train and test the content selection component
of an object description generator on a set of 393 object descriptions from the
corpus. To our knowledge, this is the first reported experiment of a trainable
content selection component for object description generation in dialogue.
Three separate content selection models that are based on the three theoretical
models, all independently achieve accuracies significantly above the majority
class baseline (17%) on unseen test data, with the intentional influences model
(42.4%) performing significantly better than either the incremental model
(30.4%) or the conceptual pact model (28.9%). But the best performing models
combine all the feature sets, achieving accuracies near 60%. Surprisingly, a
simple recency-based representation of discourse structure does as well as one
based on intentional structure. To our knowledge, this is also the first
empirical comparison of a representation of Grosz and Sidners model of
discourse structure with a simpler model for any generation task
Distinguishing Adult Pectinophora scutigera (Holdaway) According to Larval Diet by X-Ray Microanalysis
In an exploratory study using scanning electron microscope (SEM) based energy dispersive spectroscopy (EDS) of X-rays, differences were detected in the elemental compositions of adult Pectinophora scutigera raised on contrasting diets - cotton, Hibiscus tiliaceus and laboratory medium.
X-ray spectra were collected from the thorax and abdomen of 13 male and 13 female moths. X-ray yields are optimised by ashing the insects for 1 h at 400-600°C, and by operating the SEM at 25 kV.
Spectrum matching, element matching, discriminant analysis and principal components analysis were used to classify the specimens on the basis of diet with 54-100% success. Spectra were considered as a whole or processed using either a digital filter to remove background or a ZAF program to compute semiquantitative elemental concentrations. Background corrected peaks is the favoured data format, having high discriminating power and being simple to obtain and interpret.
Better classification is apparent when subsets of the same sex, body part or both are employed; and when the data for each element is normalised to a mean of 0 and a standard deviation of 1. The chief discriminating elements appear to be F, Na, Mg, P, Cl, K and Ca with Si, S, Mn, Fe and Zn being of little assistance
16S rRNA gene-based profiling of the human infant gut microbiota is strongly influenced by sample processing and PCR primer choice
Acknowledgements The authors acknowledge the assistance of Grietje Holtrop (RINH-BioSS) with the statistical analysis of the data and the Wellcome Trust Sanger Instituteâs 454 pyrosequencing team for generating 16S rRNA gene data. AWW, PS and JP received core funding support from the Wellcome Trust [grant number 098051]. AWW, JCM, HJF and KPS are funded by the Scottish Government (SG-RESAS).Peer reviewedPublisher PD
Casimir force acting on magnetodielectric bodies embedded in media
Within the framework of macroscopic quantum electrodynamics, general
expressions for the Casimir force acting on linearly and causally responding
magnetodielectric bodies that can be embedded in another linear and causal
magnetodielectric medium are derived. Consistency with microscopic
harmonic-oscillator models of the matter is shown. The theory is applied to
planar structures and proper generalizations of Casimir's and Lifshitz-type
formulas are given.Comment: 15 pages, 2 figures; minor additions and corrections, to appear in
PR
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