We study the density field around zem > 4 quasars using high‐quality medium spectral resolution Echelle Spectrograph and Imager–Keck spectra (R∼ 4300, signal‐to‐noise ratio (S/N) > 25) of 45 high‐redshift quasars selected from a total of 95 spectra. This large sample considerably increases the statistics compared to previous studies. The redshift evolution of the mean photoionization rate and the median optical depth of the intergalactic medium (IGM) are derived statistically from the observed transmitted flux and the pixel optical depth probability distribution function, respectively. This is used to study the so‐called proximity effect, that is, the observed decrease of the median optical depth of the IGM in the vicinity of the quasar caused by enhanced photoionization rate due to photons emitted by the quasar. We show that the proximity effect is correlated with the luminosity of the quasars, as expected. By comparing the observed decrease of the median optical depth with the theoretical expectation, we find that the optical depth does not decrease as rapidly as expected when approaching the quasar if the gas in its vicinity is part of the standard IGM. We interpret this effect as revealing gaseous overdensities on scales as large as ∼15 h−1 Mpc. The mean overdensity is of the order of 2 and 5 within, respectively, 10 and 3 h−1 Mpc. If true, this would indicate that high‐redshift quasars are located in the centre of overdense regions that could evolve with time into massive clusters of galaxies. The overdensity is correlated with luminosity: brighter quasars show higher overdensities.

We present the results of a survey of damped (DLA, log N(H i) > 20.3) and sub-damped Lyman-α systems (19.5 < log N(H i) < 20.3) at z > 2.55 along the lines-of-sight to 77 quasars with emission redshifts in the range 4 < z em < 6.3. Intermediate resolution (R ∼ 4300) spectra were obtained with the Echellette Spectrograph and Imager (ESI) mounted on the Keck telescope. A total of 100 systems with log N(H i) > 19.5 were detected of which 40 systems are damped Lyman-α systems for an absorption length of ΔX = 378. About half of the lines of sight of this homogeneous survey have never been investigated for DLAs. We study the evolution with redshift of the cosmological density of the neutral gas and find, consistent with previous studies at similar resolution, that Ω DLA,H I decreases at z > 3.5. The overall cosmological evolution of Ω H I shows a peak around this redshift. The H i column density distribution for log N(H i) ≥ 20.3 is fitted, consistent with previous surveys, with a single power-law of index α ∼ −1.8 ± 0.25. This power-law overpredicts data at the high-end and a second, much steeper, power-law (or a gamma function) is needed. There is a flattening of the function at lower H i column densities with an index of α ∼ −1.4 for the column density range log N(H i) = 19.5−21. The fraction of H i mass in sub-DLAs is of the order of 30%. The H i column density distribution does not evolve strongly from z ∼ 2.5 to z ∼ 4.5.

We present the elemental abundance and H 2 content measurements of a Damped Lyman-α (DLA) system with an extremely large H i column density, log N (H i) (cm −2 ) = 22.0±0.10, at z abs = 3.287 towards the QSO SDSS J 081634+144612. We measure column densities of H 2 , C i, C i ⋆ , Zn ii, Fe ii, Cr ii, Ni ii and Si ii from a high signal-to-noise and high spectral resolution VLT-UVES spectrum. The overall metallicity of the system is [Zn/H] = −1.10 ± 0.10 relative to solar. Two molecular hydrogen absorption components are seen at z = 3.28667 and 3.28742 (a velocity separation of ≈ 52 km s −1 ) in rotational levels up to J = 3. We derive a total H 2 column density of log N (H 2 ) (cm −2 ) = 18.66 and a mean molecular fraction of f = 2N (H 2 )/[2N (H 2 )+ N (H i)] = 10 −3.04±0.37 , typical of known H 2 -bearing DLA systems. From the observed abundance ratios we conclude that dust is present in the Interstellar Medium (ISM) of this galaxy, with a enhanced abundance in the H 2 -bearing clouds. However, the total amount of dust along the line of sight is not large and does not produce any significant reddening of the background QSO. The physical conditions in the H 2 -bearing clouds are constrained directly from the column densities of H 2 in different rotational levels, C i and C i ⋆ . The kinetic temperature is found to be T ≈ 75 K and the particle density lies in the range n H = 50−80 cm −3 . The neutral hydrogen column density of this DLA is similar to the mean H i column density of DLAs observed at the redshift of γ-ray bursts (GRBs). We explore the relationship between GRB-DLAs and high column density end of QSO-DLAs finding that the properties (metallicity and depletion) of DLAs with log N (H i) > 21.5 in the two populations do not appear to be significantly different.

BackgroundCurrent methods to assess the gestational age during prenatal care or at birth are a global challenge. Disadvantages, such as low accessibility, high costs, and imprecision of clinical tests and ultrasonography measurements, may compromise health decisions at birth, based on the gestational age. Newborns’ organs and tissues can indirectly indicate their physical maturity, and we hypothesized that evolutionary changes in their skin, detected using an optoelectronic device meter, may aid in estimating the gestational age. This study analyzed the feasibility of using newborn skin reflectance to estimate the gestational age at birth noninvasively.Methods and findingsA cross-sectional study evaluated the skin reflectance of selected infants, preferably premature, at birth. The first-trimester ultrasound was the reference for gestational age. A prototype of a new noninvasive optoelectronic device measured the backscattering of light from the skin, using a light emitting diode at wavelengths of 470 nm, 575 nm, and 630 nm. Univariate and multivariate regression analysis models were employed to predict gestational age, combining skin reflectance with clinical variables for gestational age estimation. The gestational age at birth of 115 newborns from 24.1 to 41.8 weeks of gestation correlated with the light at 630 nm wavelength reflectance 3.3 mm/6.5 mm ratio distant of the sensor, at the forearm and sole (Pearson’s correlation = 0.505, P < 0.001 and 0.710, P < 0.001, respectively). The best-combined variables to predict the gold standard gestational age at birth was the skin reflectance at wavelengths of 630 nm and 470 nm in combination with birth weight, phototherapy, and adjusted to include incubator stay, and sex (R2 = 0.828, P < 0.001). The main limitation of the study is that it was very specific to the premature population we studied and needs to be studied in a broader spectrum of newborns.ConclusionsA novel automated skin reflectometer device, in combination with clinical variables, was able to predict the gestational age and could be useful when the information is in doubt or is unknown. Multivariable predictive models associated the skin reflectance with easy to obtain clinical parameters, at the birth scenario. External validation needs to be proven in an actual population with the real incidence of premature infants.

BackgroundNew methodologies to estimate gestational age (GA) at birth are demanded to face the limited access to obstetric ultrasonography and imprecision of postnatal scores. The study analyzed the correlation between neonatal skin thickness and pregnancy duration. Secondarily, it investigated the influence of fetal growth profiles on tissue layer dimensions.Methods and findingsIn a feasibility study, 222 infants selected at a term-to-preterm ratio of 1:1 were assessed. Reliable information on GA was based on the early ultrasonography-based reference. The thicknesses of the epidermal and dermal skin layers were examined using high-frequency ultrasonography. We scanned the skin over the forearm and foot plantar surface of the newborns. A multivariate regression model was adjusted to determine the correlation of GA with skin layer dimensions. The best model to correlate skin thickness with GA was fitted using the epidermal layer on the forearm site, adjusted to cofactors, as follows: Gestational age (weeks) = −28.0 + 12.8 Ln (Thickness) − 4.4 Incubator staying; R2 = 0.604 (P<0.001). In this model, the constant value for the standard of fetal growth was statistically null. The dermal layer thickness on the forearm and plantar surfaces had a negative moderate linear correlation with GA (R = −0.370, P<0.001 and R = −0.421, P<0.001, respectively). The univariate statistical analyses revealed the influence of underweight and overweight profiles on neonatal skin thickness at birth. Of the 222 infants, 53 (23.9%) had inappropriate fetal growths expected for their GA. Epidermal thickness was not fetal growth standard dependent as follows: 172.2 (19.8) μm for adequate for GA, 171.4 (20.6) μm for SGA, and 177.7 (15.2) μm for LGA (P = 0.525, mean [SD] on the forearm).ConclusionsThe analysis highlights a new opportunity to relate GA at birth to neonatal skin layer thickness. As this parameter was not influenced by the standard of fetal growth, skin maturity can contribute to clinical applications.