Mechanical properties of thermally-treated and recycled glass fibres

This paper investigates the effects of temperature, heating time and atmosphere on the tensile modulus and strength of thermally-treated E-glass fibres. The heating conditions that were investigated are identical to those used in thermal recycling of waste polymer matrix composite materials, and therefore this study determines the effects of the recycling process conditions on the properties of reclaimed fibreglass. The loss in fibre strength is dependent on the temperature and time of the thermal process, and large strength loss occurs under the heating conditions used for high temperature incineration of polymer composites. A phenomenological model is presented for the residual fibre strength for the temperatures and heating time of the thermal recycling process. The reduction in fibre strength is dependent on the thermal recycling atmosphere under low temperature or short heating time conditions, but at high temperatures the strength loss is the same, regardless of furnace atmosphere (ambient air, dry air or inert gas). Quantitative fractographic analysis of the fibres shows that fracture for all heat treatments is caused by surface flaws. The strength loss is most probably due to structural relaxation during thermal annealing and a secondary effect of adsorbed surface water attacking the glass by thermally-activated stress-corrosion. It is shown that large reductions in fibre strength due to thermal recycling are not recovered during composite manufacture, therefore resulting in composite materials with significantly lower strength. The reduced strength of the composite matches the reduced fibre strength following thermal recycling

Constraining the fundamental parameters of the O-type binary CPD-41degr7733

Using a set of high-resolution spectra, we studied the physical and orbital properties of the O-type binary CPD-41 7733, located in the core of \ngc. We report the unambiguous detection of the secondary spectral signature and we derive the first SB2 orbital solution of the system. The period is 5.6815 +/- 0.0015 d and the orbit has no significant eccentricity. CPD-41 7733 probably consists of stars of spectral types O8.5 and B3. As for other objects in the cluster, we observe discrepant luminosity classifications while using spectroscopic or brightness criteria. Still, the present analysis suggests that both components display physical parameters close to those of typical O8.5 and B3 dwarfs. We also analyze the X-ray light curves and spectra obtained during six 30 ks XMM-Newton pointings spread over the 5.7 d period. We find no significant variability between the different pointings, nor within the individual observations. The CPD-41 7733 X-ray spectrum is well reproduced by a three-temperature thermal mekal model with temperatures of 0.3, 0.8 and 2.4 keV. No X-ray overluminosity, resulting e.g. from a possible wind interaction, is observed. The emission of CPD-41 7733 is thus very representative of typical O-type star X-ray emission.Comment: Accepted by ApJ, 15 pages, 9 figure

Critical evaluation of magnetic field detections reported for pulsating B-type stars in the light of ESPaDOnS, Narval and reanalyzed FORS1/2 observations

Recent spectropolarimetric studies of 7 SPB and $\beta$ Cep stars have suggested that photospheric magnetic fields are more common in B-type pulsators than in the general population of B stars, suggesting a significant connection between magnetic and pulsational phenomena. We present an analysis of new and previously published spectropolarimetric observations of these stars. New Stokes $V$ observations obtained with the high-resolution ESPaDOnS and Narval instruments confirm the presence of a magnetic field in one of the stars ($\epsilon$ Lup), but find no evidence of magnetism in 5 others. A re-analysis of the published longitudinal field measurements obtained with the low-resolution FORS1/2 spectropolarimeters finds that the measurements of all stars show more scatter from zero than can be attributed to Gaussian noise, suggesting the presence of a signal and/or systematic under-estimation of error bars. Re-reduction and re-measurement of the FORS1/2 spectra from the ESO archive demonstrates that small changes in reduction procedure lead to substantial changes in the inferred longitudinal field, and substantially reduces the number of field detections at the 3$\sigma$ level. Furthermore, we find that the published periods are not unique solutions to the time series of either the original or the revised FORS1/2 data. We conclude that the reported field detections, proposed periods and field geometry models for $\alpha$ Pyx, 15 CMa, 33 Eri and V1449 Aql are artefacts of the data analysis and reduction procedures, and that magnetic fields at the reported strength are no more common in SPB/$\beta$ Cep stars than in the general population of B stars.Comment: 10 pages, 5 figures, accepted for publication in ApJ, 2012, typo correcte

Spectropolarimetry of the Classical T Tauri Star TW Hydrae

We present high resolution (R ~ 60,000) circular spectropolarimetry of the classical T Tauri star TW Hydrae. We analyze 12 photospheric absorption lines and measure the net longitudinal magnetic field for 6 consecutive nights. While no net polarization is detected the first five nights, a significant photospheric field of Bz = 149 \pm 33 G is found on the sixth night. To rule out spurious instrumental polarization, we apply the same analysis technique to several non-magnetic telluric lines, detecting no significant polarization. We further demonstrate the reality of this field detection by showing that the splitting between right and left polarized components in these 12 photospheric lines shows a linear trend with Lande g-factor times wavelength squared, as predicted by the Zeeman effect. However, this longitudinal field detection is still much lower than that which would result if a pure dipole magnetic geometry is responsible for the mean magnetic field strength of 2.6 kG previously reported for TW Hya. We also detect strong circular polarization in the He I 5876 and the Ca II 8498 emission lines, indicating a strong field in the line formation region of these features. The polarization of the Ca II line is substantially weaker than that of the He I line, which we interpret as due to a larger contribution to the Ca II line from chromospheric emission in which the polarization signals cancel. However, the presence of polarization in the Ca II line indicates that accretion shocks on Classical T Tauri stars do produce narrow emission features in the infrared triplet lines of Calcium.Comment: One tar file. The paper has 22 pages, 5 figures. Accepted by AJ on Sep 10, 200

Time-and-motion tool for the assessment of working time in tuberculosis laboratories: a multicentre study

SETTING: Implementation of novel diagnostic assays in tuberculosis (TB) laboratory diagnosis requires effective management of time and resources. OBJECTIVE: To further develop and assess at multiple centres a time-and-motion (T&M) tool as an objective means for recording the actual time spent on running laboratory assays. DESIGN: Multicentre prospective study conducted in six European Union (EU) reference TB laboratories. RESULTS: A total of 1060 specimens were tested using four laboratory assays. The number of specimens per batch varied from one to 60; a total of 64 recordings were performed. Theoretical hands-on times per specimen (TTPS) in h:min:s for Xpert® MTB/RIF, mycobacterial interspersed repetitive unit-variable number of tandem repeats genotyping, Ziehl-Neelsen staining and manual fluorescence microscopy were respectively 00:33:02 ± 00:12:32, 00:13:34 ± 00:03:11, 00:09:54 ± 00:00:53 and 00:06:23 ± 00:01:36. Variations between laboratories were predominantly linked to the time spent on reporting and administrative procedures. Processing specimens in batches could help save time in highly automated assays (e.g., line-probe) (TTPS 00:14:00 vs. 00:09:45 for batches comprising 7 and 31 specimens, respectively). CONCLUSIONS: The T&M tool can be considered a universal and objective methodology contributing to workload assessment in TB diagnostic laboratories. Comparison of workload between laboratories could help laboratory managers justify their resource and personnel needs for the implementation of novel, time-saving, cost-effective technologies, as well as identify areas for improvement

The variation of the magnetic field of the Ap star HD~50169 over its 29 year rotation period

Context. The Ap stars that rotate extremely slowly, with periods of decades to centuries, represent one of the keys to the understanding of the processes leading to the differentiation of stellar rotation. Aims. We characterise the variations of the magnetic field of the Ap star HD 50169 and derive constraints about its structure. Methods. We combine published measurements of the mean longitudinal field of HD 50169 with new determinations of this field moment from circular spectropolarimetry obtained at the 6-m telescope BTA of the Special Astrophysical Observatory of the Russian Academy of Sciences. For the mean magnetic field modulus , literature data are complemented by the analysis of ESO spectra, both newly acquired and from the archive. Radial velocities are also obtained from these spectra. Results. We present the first determination of the rotation period of HD 50169, Prot = (29.04+/-0.82) y. HD 50169 is currently the longest-period Ap star for which magnetic field measurements have been obtained over more than a full cycle. The variation curves of both and have a significant degree of anharmonicity, and there is a definite phase shift between their respective extrema. We confirm that HD 50169 is a wide spectroscopic binary, refine its orbital elements, and suggest that the secondary is probably a dwarf star of spectral type M. Conclusions. The shapes and mutual phase shifts of the derived magnetic variation curves unquestionably indicate that the magnetic field of HD 50169 is not symmetric about an axis passing through its centre. Overall, HD 50169 appears similar to the bulk of the long-period Ap stars.Comment: 10 pages, 3 figures, accepted for publication in A&

The massive star binary fraction in young open clusters - II. NGC 6611 (Eagle Nebula)

Based on a set of over 100 medium- to high-resolution optical spectra collected from 2003 to 2009, we investigate the properties of the O-type star population in NGC6611 in the core of the Eagle Nebula (M16). Using a much more extended data set than previously available, we revise the spectral classification and multiplicity status of the nine O-type stars in our sample. We confirm two suspected binaries and derive the first SB2 orbital solutions for two systems. We further report that two other objects are displaying a composite spectrum, suggesting possible long-period binaries. Our analysis is supported by a set of Monte-Carlo simulations, allowing us to estimate the detection biases of our campaign and showing that the latter do not affect our conclusions. The absolute minimal binary fraction in our sample is f_min=0.44 but could be as high as 0.67 if all the binary candidates are confirmed. As in NGC6231 (see Paper I), up to 75% of the O star population in NGC6611 are found in an O+OB system, thus implicitly excluding random pairing from a classical IMF as a process to describe the companion association in massive binaries. No statistical difference could be further identified in the binary fraction, mass-ratio and period distributions between NGC6231 and NGC6611, despite the difference in age and environment of the two clusters.Comment: Accepted by MNRAS; 15 pages, 17 fi

Cortical Coupling Reflects Bayesian Belief Updating in the Deployment of Spatial Attention

The deployment of visuospatial attention and the programming of saccades are governed by the inferred likelihood of events. In the present study, we combined computational modeling of psychophysical data with fMRI to characterize the computational and neural mechanisms underlying this flexible attentional control. Sixteen healthy human subjects performed a modified version of Posner's location-cueing paradigm in which the percentage of cue validity varied in time and the targets required saccadic responses. Trialwise estimates of the certainty (precision) of the prediction that the target would appear at the cued location were derived from a hierarchical Bayesian model fitted to individual trialwise saccadic response speeds. Trial-specific model parameters then entered analyses of fMRI data as parametric regressors. Moreover, dynamic causal modeling (DCM) was performed to identify the most likely functional architecture of the attentional reorienting network and its modulation by (Bayes-optimal) precision-dependent attention. While the frontal eye fields (FEFs), intraparietal sulcus, and temporoparietal junction (TPJ) of both hemispheres showed higher activity on invalid relative to valid trials, reorienting responses in right FEF, TPJ, and the putamen were significantly modulated by precision-dependent attention. Our DCM results suggested that the precision of predictability underlies the attentional modulation of the coupling of TPJ with FEF and the putamen. Our results shed new light on the computational architecture and neuronal network dynamics underlying the context-sensitive deployment of visuospatial attention. Copyright \ua9 2015 Vossel et al

Modelling the incomplete Paschen-Back effect in the spectra of magnetic Ap stars

We present first results of a systematic investigation of the incomplete Paschen-Back effect in magnetic Ap stars. A short overview of the theory is followed by a demonstration of how level splittings and component strengths change with magnetic field strength for some lines of special astrophysical interest. Requirements are set out for a code which allows the calculation of full Stokes spectra in the Paschen-Back regime and the behaviour of Stokes I and V profiles of transitions in the multiplet 74 of FeII is discussed in some detail. It is shown that the incomplete Paschen-Back effect can lead to noticeable line shifts which strongly depend on total multiplet strength, magnetic field strength and field direction. Ghost components (which violate the normal selection rule on J) show up in strong magnetic fields but are probably unobservable. Finally it is shown that measurements of the integrated magnetic field modulus $H_s$ are not adversely affected by the Paschen-Back effect, and that there is a potential problem in (magnetic) Doppler mapping if lines in the Paschen-Back regime are treated in the Zeeman approximation.Comment: 8 pages, 10 figures, to appear in MNRA