3,061 research outputs found
The latest results from the ATLAS experiment
With the LHC start-up and the first runs at 900GeV, 2.36TeV
and 7TeV centre-of-mass energy in the years 2009 and 2010, the ATLAS detector started to record its first collision events. The delivered integrated luminosity has now reached 3.69 pb−1. These data have been used to perform detailed studies on the performance of the detector, including measuring charged and neutral particle mass resonances and the study of QCD cross-sections. The data have already made it possible to commission and calibrate the various ATLAS subdetectors, and understand their performance in detail. The first observation of Standard Model electroweak processes, in particular mass resonances, is also being used as a benchmark for validating the analysis and simulation tools. The status and performance of the detector is briefly reviewed, the latest physics results are summarized and limits on new physics are given
X-ray flares in Orion young stars. I. Flare characteristics
Pre-main sequence (PMS) stars are known to produce powerful X-ray flares
which resemble magnetic reconnection solar flares scaled by factors up to 10^4.
However, numerous puzzles are present including the structure of X-ray emitting
coronae and magnetospheres, effects of protoplanetary disks, and effects of
stellar rotation. To investigate these issues in detail, we examine 216 of the
brightest flares from 161 PMS stars observed in the Chandra Orion Ultradeep
Project (COUP). These constitute the largest homogeneous dataset of PMS, or
indeed stellar flares at any stellar age, ever acquired. Our effort is based on
a new flare spectral analysis technique that avoids nonlinear parametric
modeling. It can be applied to much weaker flares and is more sensitive than
standard methods. We provide a catalog with >30 derived flare properties and an
electronic atlas for this unique collection of stellar X-ray flares. The
current study (Paper I) examines the flare morphologies, and provides general
comparison of COUP flare characteristics with those of other active X-ray stars
and the Sun. Paper II will concentrate on relationships between flare behavior,
protoplanetary disks, and other stellar properties. Several results are
obtained. First, the COUP flares studied here are among the most powerful,
longest, and hottest stellar X-ray flares ever studied. Second, no significant
statistical differences in peak flare luminosity or temperature distributions
are found among different morphological flare classes, suggesting a common
underlying mechanism for all flares. Third, comparison with the general
solar-scaling laws indicates that COUP flares may not fit adequately proposed
power-temperature and duration-temperature solar-stellar fits. Fourth, COUP
super-hot flares are found to be brighter but shorter than ... ABRIDGEDComment: Accepted for publication in ApJ (07/11/08); 63 pages, 16 figures, 4
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Detailed diagnostics of an X-ray flare in the single giant HR 9024
We analyze a 96 ks Chandra/HETGS observation of the single G-type giant HR
9024. The high flux allows us to examine spectral line and continuum
diagnostics at high temporal resolution, to derive plasma parameters. A
time-dependent 1D hydrodynamic model of a loop with half-length cm (), cross-section radius
cm, with a heat pulse of 15 ks and ~erg cm s
deposited at the loop footpoints, satisfactorily reproduces the observed
evolution of temperature and emission measure, derived from the analysis of the
strong continuum emission. For the first time we can compare predictions from
the hydrodynamic model with single spectral features, other than with global
spectral properties. We find that the model closely matches the observed line
emission, especially for the hot ( K) plasma emission of the FeXXV
complex at \AA. The model loop has and aspect
ratio as typically derived for flares observed in active stellar
coronae, suggesting that the underlying physics is the same for these very
dynamic and extreme phenomena in stellar coronae independently on stellar
parameters and evolutionary stage.Comment: 26 pages. Accepted for publication on the Astrophysical Journa
Resistance to anaplastic lymphoma kinase inhibitors: Knowing the enemy is half the battle won
Geometry Diagnostics of a Stellar Flare from Fluorescent X-rays
We present evidence of Fe fluorescent emission in the Chandra HETGS spectrum
of the single G-type giant HR 9024 during a large flare. In analogy to solar
X-ray observations, we interpret the observed Fe K line as being
produced by illumination of the photosphere by ionizing coronal X-rays, in
which case, for a given Fe photospheric abundance, its intensity depends on the
height of the X-ray source. The HETGS observations, together with 3D Monte
Carlo calculations to model the fluorescence emission, are used to obtain a
direct geometric constraint on the scale height of the flaring coronal plasma.
We compute the Fe fluorescent emission induced by the emission of a single
flaring coronal loop which well reproduces the observed X-ray temporal and
spectral properties according to a detailed hydrodynamic modeling. The
predicted Fe fluorescent emission is in good agreement with the observed value
within observational uncertainties, pointing to a scale height \rstar. Comparison of the HR 9024 flare with that recently observed on II
Peg by Swift indicates the latter is consistent with excitation by X-ray
photoionization.Comment: accepted for publication on the Astrophysical Journal Letter
The Soft X-ray Lightcurves of Partially Eclipsed Stellar Flares
Most stellar flares' soft X-ray lightcurves possess a `typical' morphology,
which consists of a rapid rise followed by a slow exponential decay. However, a
study of 216 of the brightest flares on 161 pre-main sequence stars, observed
during the Chandra Orion-Ultradeep Project (COUP), showed that many flare
lightcurves depart from this typical morphology. While this can be attributed
to the superposition of multiple typical flares, we explore the possibility
that the time-variable eclipsing of flares by their host stars may also be an
important factor. We assume each flare is contained within a single, uniform
plasma density magnetic loop and specify the intrinsic variation of the flare's
emission measure with time. We consider rotational eclipse by the star itself,
but also by circumstellar discs and flare-associated prominences. Based on this
simple model, we generate a set of flares similar to those observed in the COUP
database. Many eclipses simply reduce the flare's maximum emission measure or
decay time. We conclude therefore that eclipses often pass undetected, but
usually have only a modest influence on the flare emission measure profile and
hence the derived loop lengths. We show that eclipsing can easily reproduce the
observed atypical flare morphologies. The number of atypical modelled flare
morphologies is however much less than that found in the COUP sample. The large
number of observed atypical flare morphologies, therefore, must be attributed
to other processes such as multiple flaring loops.Comment: 11 pages, 9 figure
Evolution of fermenting microbiota in tarhana produced under controlled technological conditions
The purpose of this study was to evaluate the evolution of lactic acid bacteria (LAB) and yeasts during the fermentation of tarhana produced with some pasteurised ingredients and carried out at 30 and 40 C. The chemical parameters were those typical for tarhana production. Coliform bacteria were not detected during fermentation, while LAB and yeasts were in the range 107e108 colony forming units (CFU) g 1. Plate counts showed an optimal development of both fermenting microbial groups and the differences in cell concentrations were not significant (P > 0.05). LAB were isolated during fermentation and grouped on the basis of phenotypic and polymorphic characteristics. LAB isolates were identified by a combined genetic approach consisting of 16S/23S rRNA intergenic spacer region (ITS) and partial 16S rRNA gene sequencing as Pediococcus acidilactici, Lactobacillus plantarum and Lactobacillus brevis. Hence, the pas- teurisation of the vegetable ingredients, excluded wheat flour, enhanced the hygienic conditions of tarhana without influencing the normal evolution of LAB. However, the fermentation at 40 C favoured pediococci, while the production at 30 C was mainly characterised by lactobacilli. Yeasts, identified by the restriction fragment length polymorphism (RFLP) of the 5.8S ITS rRNA gene, were mainly represented by the species Saccharomyces cerevisiae in both productions
Long‐Term prognosis in children with hypertrophic cardiomyopathy: An analysis of 37 patients aged ≤ 14 years at diagnosis
The relation of clinical, electrocardiographic, and hemodynamic findings at diagnosis to presenting features and prognosis of hypertrophic cardiomyopathy in childhood was evaluated in 37 consecutive patients below 14 years of age at time of diagnosis (24 males and 13 females, mean age 7 +/- 4 years). A left ventricular out-flow tract gradient (mean 42 +/- 27 mmHg) was detected at cardiac catheterization in 13 (35%) patients. Clinical, electrocardiographic, and hemodynamic features in patients with and without a pressure gradient were similar. Patients who had moderate to severe functional limitation had a higher incidence of syncopal episodes (p less than 0.001), lower ejection fraction (p less than 0.01), raised pulmonary artery pressure (p less than 0.001), and left ventricular end-diastolic pressure (p less than 0.01). During a follow-up of 9.2 +/- 5.1 years (range 2-18), 9 (24%) patients died suddenly (2 with a recorded left ventricular outflow tract gradient). Univariate analysis showed that reduced ejection fraction (p = 0.0001), syncopal episodes (p = 0.003), increased left ventricular end-diastolic pressure (p = 0.03), and severe dyspnea (p = 0.04) were associated with a poor prognosis. However, multivariate analysis revealed ejection fraction (p = 0.0001) and syncopal episodes (p = 0.0097) as independent predictors of survival. In conclusion, sudden cardiac death was common and was well predicted by the combination of left ventricular dysfunction and syncope at time of diagnosis
Antibiotic susceptibility profile and tetracycline resistance genes detection in salmonella spp. Strains isolated from animals and food
Salmonella spp. is among the leading causes of foodborne infections in humans and a large number of animals. Salmonella spp. is a pathogen involved in the dissemination of antimicrobial resistance because it can accumulate antibiotic resistance genes (ARGs). In this study, the antibiotic resistance profile to 15 antibiotics, belonging to six different classes, of 60 strains of Salmonella spp. collected from pets, farm animals, wildlife, and food in Sicily (Italy) was investigated by the Kirby-Bauer method. Given that almost 33.3% of the Salmonella spp. strains were resistant to tetracycline, Real-Time PCR analysis was applied on all the 60 strains to detect the presence of eight selected tet resistance genes. Besides, the presence of the int1 gene, related to the horizontal gene transfer among bacteria, was also investigated in all the strains by Real-Time PCR analysis. Our data showed that 56% of the isolated strains harbored one or more tet resistance genes and that these strains were most frequently isolated from animals living in close contact with humans. Concerning int1, 17 strains (28.3%) harbored this genetic element and eight of these simultaneously contained tet genes. The results of this study highlight the importance of using a molecular approach to detect resistance genetic determinants, whose spread can increase the diffusion of multidrug-resistant strains. Besides, the study of zoonotic bacteria such as Salmonella spp. which significantly contribute to ARGs dissemination should always follow a One Health approach that considers the health of humans, animals, and the environment to be closely related
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