Wall-bounded turbulent flows at high Reynolds numbers: Recent advances and key issues

Wall-bounded turbulent flows at high Reynolds numbers have become an increasingly active area of research in recent years. Many challenges remain in theory, scaling, physical understanding, experimental techniques, and numerical simulations. In this paper we distill the salient advances of recent origin, particularly those that challenge textbook orthodoxy. Some of the outstanding questions, such as the extent of the logarithmic overlap layer, the universality or otherwise of the principal model parameters such as the von Kármán “constant,” the parametrization of roughness effects, and the scaling of mean flow and Reynolds stresses, are highlighted. Research avenues that may provide answers to these questions, notably the improvement of measuring techniques and the construction of new facilities, are identified. We also highlight aspects where differences of opinion persist, with the expectation that this discussion might mark the beginning of their resolution

The Primordial Abundance of He4: An Update

We include new data in an updated analysis of helium in low metallicity extragalactic HII regions with the goal of deriving the primordial abundance of He4 (Y_P). We show that the new observations of Izotov et al (ITL) are consistent with previous data. However they should not be taken in isolation to determine (Y_P) due to the lack of sufficiently low metallicity points. We use the extant data in a semi-empirical approach to bounding the size of possible systematic uncertainties in the determination of (Y_P). Our best estimate for the primordial abundance of He4 assuming a linear relation between He4 and O/H is Y_P = 0.230 \pm 0.003 (stat) based on the subset of HII regions with the lowest metallicity; for our full data set we find Y_P = 0.234 \pm 0.002 (stat). Both values are entirely consistent with our previous results. We discuss the implications of these values for standard big bang nucleosynthesis (SBBN), particularly in the context of recent measurements of deuterium in high redshift, low metallicity QSO absorption-line systems.Comment: 26 pages, latex, 6 ps figure

The He abundance in the metal-deficient blue compact dwarf galaxies Tol 1214-277 and Tol 65

We present high-quality Keck telescope spectroscopic observations of the two metal-deficient blue compact dwarf (BCD) galaxies Tol 1214-277 and Tol 65. These data are used to derive the heavy-element and helium abundances. We find that the oxygen abundances in Tol 1214-277 and Tol 65 are the same, 12+logO/H=7.54+/-0.01, or Zsun/24, despite the different ionization conditions in these galaxies. The nitrogen-to-oxygen abundance ratio in both galaxies is logN/O=-1.64+/-0.02 and lies in the narrow range found for the other most metal-deficient BCDs. We use the five strongest HeI emission lines 3889, 4471, 5876, 6678 and 7065, to correct self-consistently their intensities for collisional and fluorescent enhancement mechanisms and to derive the He abundance. Underlying stellar absorption is found to be important for the HeI 4471 emission line in both galaxies, being larger in Tol 65. The weighted He mass fractions in Tol 1214-277 and Tol 65 are respectively Y=0.2458+/-0.0039 and 0.2410+/-0.0050 when the three HeI emission lines, 4471, 5876 and 6678, are used, and are, respectively, 0.2466+/-0.0043 and 0.2463+/-0.0057 when the HeI 4471 emission line is excluded. These values are in very good agreement with recent measurements of the He mass fraction in others of the most metal-deficient BCDs by Izotov and coworkers. We find that the combined effect of the systematic uncertainties due to the underlying HeI stellar absorption lines, ionization and temperature structure of the HII region and collisional excitation of the hydrogen emission lines is likely small, not exceeding ~2% (the error is 2sigma). Our results support the validity of the standard big bang model of nucleosynthesis.Comment: 22 pages, 3 Postscript figures, accepted for publication in the Astrophysical Journa

Improving Predictions for Helium Emission Lines

We have combined the detailed He I recombination model of Smits with the collisional transitions of Sawey & Berrington in order to produce new accurate helium emissivities that include the effects of collisional excitation from both the 2 (3)S and 2 (1) S levels. We present a grid of emissivities for a range of temperature and densities along with analytical fits and error estimates. Fits accurate to within 1% are given for the emissivities of the brightest lines over a restricted range for estimates of primordial helium abundance. We characterize the analysis uncertainties associated with uncertainties in temperature, density, fitting functions, and input atomic data. We estimate that atomic data uncertainties alone may limit abundance estimates to an accuracy of 1.5%; systematic errors may be greater than this. This analysis uncertainty must be incorporated when attempting to make high accuracy estimates of the helium abundance. For example, in recent determinations of the primordial helium abundance, uncertainties in the input atomic data have been neglected.Comment: ApJ, accepte

Different Vancomycin Immunoassays Contribute to the Variability in Vancomycin Trough Measurements in Neonates

Substantial interassay variability (up to 20%) has been described for vancomycin immunoassays in adults, but the impact of neonatal matrix is difficult to quantify because of blood volume constraints in neonates. However, we provide circumstantial evidence for a similar extent of variability. Using the same vancomycin dosing regimens and confirming similarity in clinical characteristics, vancomycin trough concentrations measured by PETINIA (2011-2012, n = 400) were 20% lower and the mean difference was 1.93 mg/L compared to COBAS (2012-2014, n = 352) measurements. The impact of vancomycin immunoassays in neonatal matrix was hereby suggested, supporting a switch to more advanced techniques (LC-MS/MS)

Systematic effects and a new determination of the primordial abundance of 4He and dY/dZ from observations of blue compact galaxies

We use spectroscopic observations of a sample of 82 HII regions in 76 blue compact galaxies to determine the primordial helium abundance Yp and the slope dY/dZ from the Y-O/H linear regression. To improve the accuracy of the dY/dZ measurement, we have included new spectrophotometric observations of 33 HII regions which span a large metallicity range, with oxygen abundance 12+log(O/H) varying between 7.43 and 8.30 (Zsun/30<Z<Zsun/4). For a subsample of 7 HII regions, we derive the He mass fraction taking into account known systematic effects, including collisional and fluorescent enhancements of HeI emission lines, collisional excitation of hydrogen emission, underlying stellar HeI absorption and the difference between the temperatures Te(HeII) in the He^+ zone and Te(OIII) derived from the collisionally excited [OIII] lines. We find that the net result of all the systematic effects combined is small, changing the He mass fraction by less than 0.6%. By extrapolating the Y vs. O/H linear regression to O/H=0 for 7 HII regions of this subsample, we obtain Yp=0.2421+/-0.0021 and dY/dO=5.7+/-1.8, which corresponds to dY/dZ=3.7+/-1.2, assuming the oxygen mass fraction to be O=0.66Z. In the framework of the standard Big Bang nucleosynthesis theory, this Yp corresponds to Omega_b h^2 = 0.012^+0.003_-0.002, where h is the Hubble constant in units of 100 km/s/Mpc. This is smaller at the 2sigma level than the value obtained from recent deuterium abundance and microwave background radiation measurements. The linear regression slope dY/dO=4.3+/-0.7 (corresponding to dY/dZ=2.8+/-0.5) for the whole sample of 82 HII regions is similar to that derived for the subsample of 7 HII regions, although it has a considerably smaller uncertainty.Comment: 53 pages, 3 Postscript figures, accepted for publication in the Astrophysical Journa

Detection of new sources of methanol emission at 107 and 108 GHz with the Mopra telescope

A southern hemisphere survey of methanol emission sources in two millimeter wave transitions has been carried out using the ATNF Mopra millimetre telescope. Sixteen emission sources have been detected in the 3(1)-4(0)A+ transition of methanol at 107 GHz, including six new sources exhibiting class II methanol maser emission features. Combining these results with the similar northern hemisphere survey, a total of eleven 107-GHz methanol masers have been detected. A survey of the methanol emission in the 0(0)-1(-1)E transition at 108 GHz resulted in the detection of 16 sources; one of them showing maser characteristics. This is the first methanol maser detected at 108 GHz, presumably of class II. The results of LVG statistical equilibrium calculations confirm the classification of these new sources as a class II methanol masers.Comment: 11 pages, 6 figures, accepted for publication in MNRAS, mn.sty include

Development of fundamental motor skills between 2006 and 2016 in Dutch primary school children

Background: Fundamental Motor Skills (FMS) are important building blocks for children’s sport-participation and lifelong physical activity. In the last decade, several international studies have reported delays in the development of FMS. To get better insight into the Dutch situation and to provide future directions, this study examined the development of FMS in Dutch primary school children.Method: The main goal of this study is to compare FMS of 11–12-year-old Dutch children in 2016 with scores of similarly-aged-children in 2006. In addition, gender, age, BMI were taken into account, to see whether changes in motor performance are related to these child characteristics. FMS-test scores on seven motor competence tests (balance, swing, jump, roll, shoot, throwing and catching, and tennis) from 1939 children in 2016 were set side by side with those of 1648 children in 2006. Temporal changes in motor competence scores were analyzed using regression-analysis.Results: This cross-sectional study shows better results for the children in 2006 compared to similarly-aged-children in 2016. Lower scores were found on six out of seven tested FMS, with the largest declines on the object control skills tennis and throwing and catching. Only vaulting jump skills remained on the same level. Overall, children with a higher BMI scored lower on all tests, except for throwing and catching via the wall. On the balancing, jumping and tennis test, the gap with children with a lower BMI widened over the last decade. Girls showed a lower competence level on rolling, shooting and throwing and catchingcompared to boys. During the last decade, their performance on the tennis test decreased more than for boys. Conclusions: Results of this study are alarming as diminishing motor skills are related to lower sport participation and poorer health outcomes. For the future generation, new interventions are needed to help children reach a sufficient proficiency level in FMS, to prevent or overcome the negative effects of lowered motor skills. Targeting FMS components during physical education and outside of school hours may potentially be a valuable strategy in reverting the lowering FMS levels amongst childre