Sign-time distribution for a random walker with a drifting boundary

We present a derivation of the exact sign-time distribution for a random walker in the presence of a boundary moving with constant velocity.Comment: 5 page

Short-term health effects in the general population following a major train accident with acrylonitrile in Belgium

Background: Following a train derailment, several tons of acrylonitrile (ACN) exploded, inflamed and part of the ACN ended up in the sewage system of the village of Wetteren. More than 2000 residents living in the close vicinity of the accident and along the sewage system were evacuated. A human biomonitoring study of the adduct N-2-cyanoethylvaline (CEV) was carried out days 14-21 after the accident. Objectives: (1) To describe the short-term health effects that were reported by the evacuated residents following the train accident, and (2) to explore the association between the CEV concentrations, extrapolated at the time of the accident, and the self-reported short-term health effects. Methods: Short-term health effects were reported in a questionnaire (n=191). An omnibus test of independence was used to investigate the association between the CEV concentrations and the symptoms. Dose-response relationships were quantified by Generalized Additive Models (GAMs). Results: The most frequently reported symptoms were local symptoms of irritation. In non-smokers, dose-dependency was observed between the CEV levels and the self-reporting of irritation (p=0.007) and nausea (p=0.007). Almost all non-smokers with CEV concentrations above 100 pmol/g globin reported irritation symptoms. Both absence and presence of symptoms was reported by non-smokers with CEV concentrations below the reference value and up to 10 times the reference value. Residents who visited the emergency services reported more symptoms. This trend was seen for the whole range of CEV concentrations, and thus independently of the dose. Discussion and conclusion: The present study is one of the first to relate exposure levels to a chemical released during a chemical incident to short-term (self-reported) health effects. A dose-response relation was observed between the CEV concentrations and the reporting of short-term health effects in the non-smokers. Overall, the value of self-reported symptoms to assess exposure showed to be limited. The results of this study confirm that a critical view should be taken when considering self-reported health complaints and that ideally biomarkers are monitored to allow an objective assessment of exposure

Gravity-mode period spacings as seismic diagnostic for a sample of gamma Doradus stars from Kepler space photometry and high-resolution ground-based spectroscopy

Gamma Doradus stars (hereafter gamma Dor stars) are gravity-mode pulsators of spectral type A or F. Such modes probe the deep stellar interior, offering a detailed fingerprint of their structure. Four-year high-precision space-based Kepler photometry of gamma Dor stars has become available, allowing us to study these stars with unprecedented detail. We selected, analysed, and characterized a sample of 67 gamma Dor stars for which we have Kepler observations available. For all the targets in the sample we assembled high-resolution spectroscopy to confirm their F-type nature. We found fourteen binaries, among which four single-lined binaries, five double-lined binaries, two triple systems and three binaries with no detected radial velocity variations. We estimated the orbital parameters whenever possible. For the single stars and the single-lined binaries, fundamental parameter values were determined from spectroscopy. We searched for period spacing patterns in the photometric data and identified this diagnostic for 50 of the stars in the sample, 46 of which are single stars or single-lined binaries. We found a strong correlation between the spectroscopic vsini and the period spacing values, confirming the influence of rotation on gamma Dor-type pulsations as predicted by theory. We also found relations between the dominant g-mode frequency, the longest pulsation period detected in series of prograde modes, vsini, and log Teff.Comment: 61 pages, 61 figures, 6 tables, accepted for publication in ApJ

Critical dimensions of the diffusion equation

We study the evolution of a random initial field under pure diffusion in various space dimensions. From numerical calculations we find that the persistence properties of the system show sharp transitions at critical dimensions d1 ~ 26 and d2 ~ 46. We also give refined measurements of the persistence exponents for low dimensions.Comment: 4 pages, 5 figure

Mathematics difficulties in extremely preterm children : evidence of a specific deficit in basic mathematics processing

Background: Extremely preterm (EP, <26 wk gestation) children have been observed to have poor academic achievement in comparison to their term-born peers, especially in mathematics. This study investigated potential underlying causes of this difficulty. Methods: A total of 219 EP participants were compared with 153 term-born control children at 11 y of age. All children were assessed by a psychologist on a battery of standardized cognitive tests and a number estimation test assessing children’s numerical representations. Results: EP children underperformed in all tests in comparison with the term controls (the majority of Ps < 0.001). Different underlying relationships between performance on the number estimation test and mathematical achievement were found in EP as compared with control children. That is, even after controlling for cognitive ability, a relationship between number representations and mathematical performance persisted for EP children only (EP: r = 0.346, n = 186, P < 0.001; control: r = 0.095, n = 146, P = 0.256). Conclusion: Interventions for EP children may target improving children’s numerical representations in order to subsequently remediate their mathematical skills

Addressing potential sources of variation in several non-destructive techniques for measuring firmness in apples

Measurements of firmness have traditionally been carried out according to the Magness Taylor (MT) procedure; using a texture analyser or penetrometer in reference texture tests. Non-destructive tests like the acoustic impulse response of acoustic firmness sensors (AFSs), a low-mass impact firmness sensor Sinclair International (SIQ-FT) and impact test (Lateral Impact – UPM) have also been used to measure texture and firmness. The objectives of this study were to evaluate the influence of different sources of variation in these three non-destructive tests and to evaluate their respective capabilities of discriminating between fruit maturity at two different harvest dates, turgidity before and after dehydration treatment and ripening after different storage periods. According to our results, fruit studied an unexpected AFS trend with turgidity. Contact measurements (Lateral Impact – UPM and SIQ-FT) appeared highly sensitive to changes in turgidity, but were less able to follow changes in ripening caused by storage period. Contact measurements were suitable for detecting differences between fruits from different harvest dates and showed higher correlation coefficients with reference texture tests than acoustic measurements. The Lateral Impact – UPM test proved better at separating fruits according to turgidity than the SIQ-FT instrumen

Signatures of internal rotation discovered in the Kepler data of five slowly pulsating B stars

Context. Massive stars are important building blocks of the Universe, and their stellar structure and evolution models are fundamental cornerstones of various fields in modern astrophysics. The precision of these models is strongly limited by our lack of understanding of various internal mixing processes that significantly influence the lifetime of these objects, such as core overshoot, chemical mixing, or the internal differential rotation. Aims. Our goal is to calibrate models by extending the sample of available seismic studies of slowly pulsating B (SPB) stars, providing input for theoretical modelling efforts that will deliver precise constraints on the parameters describing the internal mixing processes in these objects. Methods. We used spectral synthesis and disentangling techniques to derive fundamental parameters and to determine precise orbital parameters from high-resolution spectra. We employed custom masks to construct light curves from the virtually uninterrupted four year long Kepler pixel data and used standard time-series analysis tools to construct a set of significant frequencies for each target. These sets were first filtered from combination frequencies, and then screened for period spacing patterns. Results. We detect gravity mode period series of modes, of the same degree ℓ with consecutive radial order n, in four new and one revisited SPB star. These series (covering typically 10 to 40 radial orders) are clearly influenced by moderate to fast rotation and carry signatures of chemical mixing processes. Furthermore, they are predominantly prograde dipole series. Our spectroscopic analysis, in addition to placing each object inside the SPB instability strip and identifying KIC 4930889 as an SB2 binary, reveals that KIC 11971405 is a fast rotator that shows very weak Be signatures. Together with the observed photometric outbursts this illustrates that this Be star is a fast rotating SPB star. We hypothesise that the outbursts might be connected to its very densely compressed oscillation spectrum

Analytical results for generalized persistence properties of smooth processes

We present a general scheme to calculate within the independent interval approximation generalized (level-dependent) persistence properties for processes having a finite density of zero-crossings. Our results are especially relevant for the diffusion equation evolving from random initial conditions, one of the simplest coarsening systems. Exact results are obtained in certain limits, and rely on a new method to deal with constrained multiplicative processes. An excellent agreement of our analytical predictions with direct numerical simulations of the diffusion equation is found.Comment: 21 pages, 4 figures, to appear in Journal of Physics

A search for pulsations in the HgMn star HD 45975 with CoRoT photometry and ground-based spectroscopy

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD 45975 was monitored for nearly two months by the CoRoT satellite. Independent analyses of the light curve provides evidence of monoperiodic variations with a frequency of 0.7572 c/d and a peak-to-peak amplitude of ~2800 ppm. Multisite, ground-based spectroscopic observations overlapping the CoRoT observations show the star to be a long-period, single-lined binary. Furthermore, with the notable exception of mercury, they reveal the same periodicity as in photometry in the line moments of chemical species exhibiting strong overabundances (e.g., Mn and Y). In contrast, lines of other elements do not show significant variations. As found in other HgMn stars, the pattern of variability consists in an absorption bump moving redwards across the line profiles. We argue that the photometric and spectroscopic changes are more consistent with an interpretation in terms of rotational modulation of spots at the stellar surface. In this framework, the existence of pulsations producing photometric variations above the ~50 ppm level is unlikely in HD 45975. This provides strong constraints on the excitation/damping of pulsation modes in this HgMn star.Comment: Accepted for publication in A&A, 14 pages, 15 colour figures (revised version after language editing