689 research outputs found
-Poincar\'e invariant quantum field theories with KMS weight
A natural star product for 4-d -Minkowski space is used to
investigate various classes of -Poincar\'e invariant scalar field
theories with quartic interactions whose commutative limit coincides with the
usual theory. -Poincar\'e invariance forces the integral
involved in the actions to be a twisted trace, thus defining a KMS weight for
the noncommutative (C*-)algebra modeling the -Minkowski space. The
associated modular group and Tomita modular operator are characterized. In all
the field theories, the twist generates different planar one-loop contributions
to the 2-point function which are at most UV linearly diverging. Some of these
theories are free of UV/IR mixing. In the others, UV/IR mixing shows up in
non-planar contributions to the 2-point function as a polynomial singularity at
exceptional zero external momenta while staying finite at non-zero external
momenta. These results are discussed together with the possibility for the KMS
weight relative to the quantum space algebra to trigger the appearance of KMS
state on the algebra of observables.Comment: 32 pages, several paragraphs added, published in PR
Analysis of Air Traffic Controllers Decisions
International audienceThis paper presents an approach based on a multiple criteria decision making methodology (MCDM) to analyse the decisions of Air Traffic Controllers. This study will allow to model some tools able to assist the controllers in their tasks and particularly able to help them to assume the ceaseless increase of Air Traffic. Currently the platform AMANDA assists controllers on only one sector of control. This platform was very pleasant welcome, and we wish to extend these principles to adjacent sectors, and thus include tool to help the cooperation between adjacent controllers. This analysis is composed of three main points. First it is necessary to determine the decision making process of controllers. The second point consists of the application of the MCDM which guide all the study. And finally a repertory grid technique is applied in order to support the operational aspect of MCDM and to support the interviews. We begin this paper by a presentation of Air traffic Control and the problematic, we present then AMANDA and its principles, and the objectives for the new version. In a third part we describe the approach developed and a real example of its application, the results and analyses that we can deduce of this first grid are also presented. These results must be, of course, confirmed and validated by the controllers
The Star Clusters in the Irregular Galaxy NGC 4449
We examine the star clusters in the irregular galaxy NGC 4449. We use a
near-infrared spectrum and broad-band images taken with the HST to place a
limit of 8--15 Myrs on the age of the bright central ojbect in NGC 4449. Its
luminosity and size suggest that it is comparable to young super star clusters.
However, there is a peculiar nucleated-bar structure at the center of this star
cluster, and we suggest that this structure is debris from the interaction that
has produced the counter-rotating gas systems and extended gas streamers in the
galaxy.
From the images we identify 60 other candidate compact star clusters in NGC
4449. Fourteen of these could be background elliptical galaxies or old globular
star clusters. Of the star clusters, three, in addition to the central object,
are potentially super star clusters, and many others are comparable to the
populous clusters found in the LMC. The star clusters span a large range in
ages with no obvious peak in cluster formation that might be attributed to the
interaction that the galaxy has experienced.Comment: To be published in PASP, Feb. 2001; also attainable from
ftp.lowell.edu, cd pub/dah/n4449pape
Optically variable active galactic nuclei in the 3 yr VST survey of the COSMOS field
The analysis of the variability of active galactic nuclei (AGNs) at different
wavelengths and the study of possible correlations among different spectral
windows are nowadays a major field of inquiry. Optical variability has been
largely used to identify AGNs in multivisit surveys. The strength of a
selection based on optical variability lies in the chance to analyze data from
surveys of large sky areas by ground-based telescopes. However the
effectiveness of optical variability selection, with respect to other
multiwavelength techniques, has been poorly studied down to the depth expected
from next generation surveys. Here we present the results of our r-band
analysis of a sample of 299 optically variable AGN candidates in the VST survey
of the COSMOS field, counting 54 visits spread over three observing seasons
spanning > 3 yr. This dataset is > 3 times larger in size than the one
presented in our previous analysis (De Cicco et al. 2015), and the observing
baseline is ~8 times longer. We push towards deeper magnitudes (r(AB) ~23.5
mag) compared to past studies; we make wide use of ancillary multiwavelength
catalogs in order to confirm the nature of our AGN candidates, and constrain
the accuracy of the method based on spectroscopic and photometric diagnostics.
We also perform tests aimed at assessing the relevance of dense sampling in
view of future wide-field surveys. We demonstrate that the method allows the
selection of high-purity (> 86%) samples. We take advantage of the longer
observing baseline to achieve great improvement in the completeness of our
sample with respect to X-ray and spectroscopically confirmed samples of AGNs
(59%, vs. ~15% in our previous work), as well as in the completeness of
unobscured and obscured AGNs. The effectiveness of the method confirms the
importance to develop future, more refined techniques for the automated
analysis of larger datasets.Comment: 21 pages, 10 figures; accepted for publication in A&
Méthodologie multicritÚre pour la conception d'un espace de coopération. Application au contrÎle de trafic aérien
International audienc
The Globular Cluster System of NGC4374
We study the globular cluster system (GCS) of the giant elliptical NGC4374
(M84) in the Virgo cluster using B and R photometry. The colour distribution is
bimodal with peaks at B-R=1.11 and B-R=1.36, fitting well to those found in
other early-type galaxies. The radial profile of the cluster number density is
flatter than the galaxy light. Using the luminosity function we derive a
distance modulus of , which within the uncertainty agrees with
the distance from surface brightness fluctuations. Blue and red clusters show
similar radial concentrations and azimuthal distributions. The total number of
clusters is , which together with our distance modulus leads to a
specific frequency of . This value is surprisingly low for a
giant elliptical, but resembles the case of merger remnants like NGC1316, where
the low specific frequency is probably caused by the luminosity contribution of
an intermediate-age population. A further common property is the high rate of
type Ia supernovae which also may indicate the existence of a younger
population. However, unlike in the case of NGC1316, one cannot find any further
evidence that NGC4374 indeed hosts younger populations. The low specific
frequency would also fit to a S0 galaxy seen face-on.Comment: Accepted for publication in Astronomy & Astrophysics. 11 page
Comparison of Gene Repertoires and Patterns of Evolutionary Rates in Eight Aphid Species That Differ by Reproductive Mode
In theory, the loss of sexual reproduction is expected to result in the accumulation of
deleterious mutations. In aphids, two main types of life cycle, cyclic and obligate
parthenogenesis, represent respectively âsexualâ and âasexualâ
reproductive modes. We used the complete pea aphid genome and previously published
expressed sequence tags (ESTs) from two other aphid species. In addition, we obtained
100,000 new ESTs from five more species. The final set comprised four sexual and four
asexual aphid species and served to test the influence of the reproductive mode on the
evolutionary rates of genes. We reconstructed coding sequences from ESTs and annotated
these genes, discovering a novel peptide gene family that appears to be among the most
highly expressed transcripts from several aphid species. From 203 genes found to be 1:1
orthologs among the eight species considered, we established a species tree that partly
conflicted with taxonomy (for Myzus ascalonicus). We then used this
topology to evaluate the dynamics of evolutionary rates and mutation accumulation in the
four sexual and four asexual taxa. No significant increase of the nonsynonymous to
synonymous ratio or of nonsynonymous mutation numbers was found in any of the four
branches for asexual taxa. We however found a significant increase of the synonymous rate
in the branch leading to the asexual species Rhopalosiphum maidis, which
could be due to a change in the mutation rate or to an increased number of generations
implied by its change of life cycle
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Diurnal variations of ambient particulate wood burning emissions and their contribution to the concentration of Polycyclic Aromatic Hydrocarbons (PAHs) in Seiffen, Germany
Residential wood burning is becoming an increasingly important cause of air quality problems since it has become a popular source of alternative energy to fossil fuel. In order to characterize the contribution of residential wood burning to local particle pollution, a field campaign was organized at the village of Seiffen (Saxony, Germany). During this campaign, an Aerosol Mass Spectrometer (AMS) was deployed in parallel to a PM1 high volume filter sampler. The AMS mass spectra were analyzed using Positive Matrix Factorization (PMF) to obtain detailed information about the organic aerosol (OA). Biomass-burning organic aerosol (BBOA), Hydrocarbon-like organic aerosol (HOA), and Oxygenated Organic Aerosol (OOA) were identified and represented 20%, 17% and 62% of total OA, respectively. Additionally, Polycyclic Aromatic Hydrocarbons (PAH) were measured by the AMS with an average concentration of 10 ng mâ3 and short term events of extremely high PAH concentration (up to 500 ng mâ3) compared to the mean PAH value were observed during the whole measurement period. A comparison with the results from PM1 filter samples showed that the BBOA factor and the AMS PAH are good indicators of the total concentration of the different monosaccharide anhydrides and PAH measured on the filter samples. Based on its low correlation with CO and the low car traffic, the HOA factor was considered to be related to residential heating using liquid fuel. An influence of the time of the week (week vs. weekend) on the diurnal profiles of the different OA components was observed. The weekdays were characterized by two maxima; a first one early in the morning and a stronger one in the evening. During the weekend days, the different OA components principally reached only one maximum in the afternoon. Finally, the PAH emitted directly from residential wood combustion was estimated to represent 1.5% of the total mass of the BBOA factor and around 62% of the total PAH concentration measured at Seiffen. This result highlights the important contribution of residential wood combustion to air quality and PAH emissions at the sampling place, which might have a significant impact on human health. Moreover, it also emphasizes the need for a better time resolution of the chemical characterization of toxic particulate compounds in order to provide more information on variations of the different sources through the days as well as to better estimate the real human exposure
Colloidal stability of tannins: astringency, wine tasting and beyond
Tannin-tannin and tannin-protein interactions in water-ethanol solvent
mixtures are studied in the context of red wine tasting. While tannin
self-aggregation is relevant for visual aspect of wine tasting (limpidity and
related colloidal phenomena), tannin affinities for salivary proline-rich
proteins is fundamental for a wide spectrum of organoleptic properties related
to astringency. Tannin-tannin interactions are analyzed in water-ethanol
wine-like solvents and the precipitation map is constructed for a typical grape
tannin. The interaction between tannins and human salivary proline-rich
proteins (PRP) are investigated in the framework of the shell model for
micellization, known for describing tannin-induced aggregation of beta-casein.
Tannin-assisted micellization and compaction of proteins observed by SAXS are
described quantitatively and discussed in the case of astringency
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