Frs Fnrs Postdoctoral Researcher

Belgium

Frs Fnrs Postdoctoral Researcher

Belgium

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Fossati L.,University of Bonn | Castro N.,University of Bonn | Morel T.,University of Liège | Langer N.,University of Bonn | And 17 more authors.
Astronomy and Astrophysics | Year: 2015

Only a small fraction of massive stars seem to host a measurable structured magnetic field, whose origin is still unknown and whose implications for stellar evolution still need to be assessed. Within the context of the "B fields in OB stars (BOB)" collaboration, we used the HARPSpol spectropolarimeter to observe the early B-type stars β CMa (HD44743; B1 II /III) and εCMa (HD52089; B1.5II) in December 2013 and April 2014. For both stars, we consistently detected the signature of a weak (< 30 G in absolute value) longitudinal magnetic field, approximately constant with time. We determined the physical parameters of both stars and characterise their X-ray spectrum. For the β Cep star β CMa, our mode identification analysis led to determining a rotation period of 13.6 ± 1. 2 days and of an inclination angle of the rotation axis of 57.6 ± 1.7°, with respect to the line of sight. On the basis of these measurements and assuming a dipolar field geometry, we derived a best fitting obliquity of about 22° and a dipolar magnetic field strength (Bd) of about 100 G (60 < Bd < 230 G within the 1σ level), below what is typically found for other magnetic massive stars. This conclusion is strengthened further by considerations of the star's X-ray spectrum. For εCMa we could only determine a lower limit on the dipolar magnetic field strength of 13 G. For this star, we determine that the rotation period ranges between 1.3 and 24 days. Our results imply that both stars are expected to have a dynamical magnetosphere, so the magnetic field is not able to support a circumstellar disk. We also conclude that both stars are most likely core hydrogen burning and that they have spent more than 2/3 of their main sequence lifetime. A histogram of the distribution of the dipolar magnetic field strength for the magnetic massive stars known to date does not show the magnetic field "desert" observed instead for intermediate-mass stars. The biases involved in the detection of (weak) magnetic fields in massive stars with the currently available instrumentation and techniques imply that weak fields might be more common than currently observed. Our results show that, if present, even relatively weak magnetic fields are detectable in massive stars and that more observational effort is probably still needed to properly access the magnetic field incidence. © ESO 2015.


Bouabidi A.,University of Liège | Bouabidi A.,Hassan II University | Talbi M.,Hassan II University | Bourichi H.,Hassan II University | And 7 more authors.
Drug Testing and Analysis | Year: 2012

An innovative versatile strategy using Total Error has been proposed to decide about the method's validity that controls the risk of accepting an unsuitable assay together with the ability to predict the reliability of future results. This strategy is based on the simultaneous combination of systematic (bias) and random (imprecision) error of analytical methods. Using validation standards, both types of error are combined through the use of a prediction interval or β-expectation tolerance interval. Finally, an accuracy profile is built by connecting, on one hand all the upper tolerance limits, and on the other hand all the lower tolerance limits. This profile combined with pre-specified acceptance limits allows the evaluation of the validity of any quantitative analytical method and thus their fitness for their intended purpose. In this work, the approach of accuracy profile was evaluated on several types of analytical methods encountered in the pharmaceutical industrial field and also covering different pharmaceutical matrices. The four studied examples depicted the flexibility and applicability of this approach for different matrices ranging from tablets to syrups, different techniques such as liquid chromatography, or UV spectrophotometry, and for different categories of assays commonly encountered in the pharmaceutical industry i.e. content assays, dissolution assays, and quantitative impurity assays. The accuracy profile approach assesses the fitness of purpose of these methods for their future routine application. It also allows the selection of the most suitable calibration curve, the adequate evaluation of a potential matrix effect and propose efficient solution and the correct definition of the limits of quantification of the studied analytical procedures. © 2012 John Wiley & Sons, Ltd.


Hubrig S.,Leibniz Institute for Astrophysics Potsdam | Kholtygin A.F.,Saint Petersburg State University | Scholler M.,European Southern Observatory | Anderson R.I.,University of Geneva | And 6 more authors.
Astronomische Nachrichten | Year: 2015

Our recent search for the presence of a magnetic field in the bright early A-type supergiant HD 92207 using FORS 2 in spectropolarimetric mode revealed the presence of a longitudinal magnetic field of the order of a few hundred Gauss. However, the definite confirmation of the magnetic nature of this object remained pending due to the detection of shortterm spectral variability probably affecting the position of line profiles in left- and right-hand polarized spectra. We present new magnetic field measurements of HD 92207 obtained on three different epochs in 2013 and 2014 using FORS 2 in spectropolarimetric mode. A 3σ detection of the mean longitudinal magnetic field using the entire spectrum, 〈Bz〉all = 104 ± 34 G, was achieved in observations obtained in 2014 January. At this epoch, the position of the spectral lines appeared stable. Our analysis of spectral line shapes recorded in opposite circularly polarized light, i.e. in light with opposite sense of rotation, reveals that line profiles in the light polarized in a certain direction appear slightly split. The mechanism causing such a behaviour in the circularly polarized light is currently unknown. Trying to settle the issue of short-term variability, we searched for changes in the spectral line profiles on a time scale of 8-10 min using HARPS polarimetric spectra and on a time scale of 3-4 min using time series obtained with the CORALIE spectrograph. No significant variability was detected on these time scales during the epochs studied. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Cavalier E.,University of Liège | Rozet E.,University of Liège | Rozet E.,Frs Fnrs Postdoctoral Researcher | Carlisi A.,University of Liège | And 5 more authors.
Clinical Chemistry and Laboratory Medicine | Year: 2010

Background: The goal of this study was to validate the DiaSorin Liaison BAP OSTASE, a new method for measurement of bone alkaline phosphatase (BAP), and to compare this method with the Beckman-Coulter Access Ostase. We also wanted to establish the reference range for BAP in adults and children. Methods: We determined the precision, functional sensitivity, recovery, linearity and measurement uncertainty, accuracy profile and β-expectation limits. We defined an adult reference interval using individuals with 25-OH vitamin D >80 nmol/L, parathormone <58 ng/L, and normal calcium, phosphorous and estimated glomerular filtration rate. Each adult subclass (men/non-menopausal women/menopause women) contained 120 individuals. We also determined the 2.5th and 97.5th percentiles from a population of 450 children, stratified according to age and gender. Results: The results of the validation showed: precision <6%, functional sensitivity <0.74 μg/L, mean recovery 98.8±4.2% and good linearity. Relative uncertainty ranged from 9.0% to 12.9%, and the risk of one result falling out of the ±15% acceptance limits was <5% for concentrations between 7 and 94 μg/L. The Bland-Altman plot showed no systematic bias between the two methods. In adults, we did not find any statistical difference between the different subclasses. The upper limit of normality observed in the entire population (n=360) was 21.3 μg/L (90% CI: 18.3-24.2 μg/L). Conclusions: The Liaison BAP OSTASE is a robust method, and is completely validated between 7 and 93 μg/L: in this range, 95% of the values obtained will be within ±15% of the true value. © 2010 by Walter de Gruyter Berlin New York.

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