Simple Screened Hydrogen Model of Excitons in Two-Dimensional Materials

We present a generalized hydrogen model for the binding energies ($E_B$) of excitons in two-dimensional (2D) materials that sheds light on the fundamental differences between excitons in two and three dimensions. In contrast to the well-known hydrogen model of three-dimensional (3D) excitons, the description of 2D excitons is complicated by the fact that the screening cannot be assumed to be local. We show that one can consistently define an effective 2D dielectric constant by averaging the screening over the extend of the exciton. For an ideal 2D semiconductor this leads to a simple expression for $E_B$ that only depends on the excitonic mass and the 2D polarizability $\alpha$. The model is shown to produce accurate results for 51 transition metal dichalcogenides. Remarkably, over a wide range of polarizabilities the expression becomes independent of the mass and we obtain $E_B^{2D}\approx3/(4\pi\alpha)$, which explains the recently observed linear scaling of exciton binding energies with band gap. It is also shown that the model accurately reproduces the non-hydrogenic Rydberg series in WS$_2$ and can account for screening from the environment.Comment: 5 page

A soil moisture and temperature network for SMOS validation in Western Denmark

The Soil Moisture and Ocean Salinity Mission (SMOS) acquires surface soil moisture data of global coverage every three days. Product validation for a range of climate and environmental conditions across continents is a crucial step. For this purpose, a soil moisture and soil temperature sensor network was established in the Skjern River Catchment, Denmark. The objectives of this article are to describe a method to implement a network suited for SMOS validation, and to present sample data collected by the network to verify the approach. The design phase included (1) selection of a single SMOS pixel (44 × 44 km), which is representative of the land surface conditions of the catchment and with minimal impact from open water (2) arrangement of three network clusters along the precipitation gradient, and (3) distribution of the stations according to respective fractions of classes representing the prevailing environmental conditions. Overall, measured moisture and temperature patterns could be related to the respective land cover and soil conditions. Texture-dependency of the 0–5 cm soil moisture measurements was demonstrated. Regional differences in 0–5 cm soil moisture, temperature and precipitation between the north-east and south-west were found to be small. A first comparison between the 0–5 cm network averages and the SMOS soil moisture (level 2) product is in range with worldwide validation results, showing comparable trends for SMOS retrieved soil moisture (<i>R</i><sup>2</sup> of 0.49) as well as initial soil moisture and temperature from ECMWF used in the retrieval algorithm (<i>R</i><sup>2</sup> of 0.67 and 0.97, respectively). While retrieved/initial SMOS soil moisture indicate significant under-/overestimation of the network data (biases of −0.092/0.057 m<sup>3</sup> m<sup>−3</sup>), the initial temperature is in good agreement (bias of −0.2 °C). Based on these findings, the network performs according to expectations and proves to be well-suited for its purpose. The discrepancies between network and SMOS soil moisture will be subject of subsequent studies

Impact of the COVID-19 pandemic on women's perinatal mental health and its association with personality traits: An observational study

Introduction - The burden of perinatal mental health problems was expected to increase during the COVID-19 pandemic. We prospectively investigated the impact of the COVID-19 pandemic on the mental health of pregnant and postpartum women in Norway and explored associations with their sociodemographic characteristics and personality traits. Material and methods - Sociodemographic information and the self-reported impact of pandemic on wellbeing of pregnant women was collected using an online survey. To assess women's mental health, two validated questionnaires, the Edinburgh Postpartum Depression Scale (EPDS) and the Generalized Anxiety Disorder-7 item Scale (GAD-7), were used prenatally and postnatally. Personality traits were evaluated using HumanGuide, a web-based ipsative psychological evaluation instrument. Results - 772 women were included prenatally, of which 526 also responded to the survey 4–6 weeks postnatally. The median age was 29 years, 53.6% of the women were nulliparous when enrolled, and 35.1% worked in the healthcare sector. The median EPDS (6.0; interquartile range [IQR] 3.0–10.0 vs 6.0; IQR: 3.0–10.0) and the median GAD-7 (5.0; IQR 2.0–9.0 vs 5.0; IQR 2.0–9.0) were similar pre-and postnatally. Prenatally, the proportion of women scoring ≥13 on EPDS and ≥10 on GAD-7 was 14.5% (112/772) and 21.5% (166/772), whereas the postnatal figures were 15.6% (82/526) and 21.5% (113/526), respectively. The differences were not significant (P = 0.59 and P = 0.99). Being Conclusions - During the initial phase of the COVID-19 pandemic, the prevalence of depression (EPDS ≥ 13) and anxiety (GAD-7 ≥ 10) was 14.5% and 21.5%, respectively, among Norwegian pregnant women. Certain sociodemographic characteristics and personality traits were significant predictors of depression and anxiety

Forming Realistic Late-Type Spirals in a LCDM Universe: The Eris Simulation

Simulations of the formation of late-type spiral galaxies in a cold dark matter LCDM universe have traditionally failed to yield realistic candidates. Here we report a new cosmological N-body/SPH simulation of extreme dynamic range in which a close analog of a Milky Way disk galaxy arises naturally. Termed Eris, the simulation follows the assembly of a galaxy halo of mass Mvir=7.9x10^11 Msun with a total of N=18.6 million particles (gas + dark matter + stars) within the final virial radius, and a force resolution of 120 pc. It includes radiative cooling, heating from a cosmic UV field and supernova explosions, a star formation recipe based on a high gas density threshold (nSF=5 atoms cm^-3 rather than the canonical nSF=0.1 atoms cm^-3), and neglects AGN feedback. At the present epoch, the simulated galaxy has an extended rotationally-supported disk with a radial scale length Rd=2.5 kpc, a gently falling rotation curve with circular velocity at 2.2 disk scale lenghts of V2.2=214 km/s, a bulge-to-disk ratio B/D=0.35, and a baryonic mass fraction that is 30% below the cosmic value. The disk is thin, is forming stars in the region of the Sigma_SFR - Sigma_HI plane occupied by spiral galaxies, and falls on the photometric Tully-Fisher and the stellar mass-halo virial mass relations. Hot (T>3x10^5 K), X-ray luminous halo gas makes only 26% of the universal baryon fraction and follows a flattened density profile proportional to r^-1.13 out to r=100 kpc. Eris appears then to be the first cosmological hydrodynamic simulation in which the galaxy structural properties, the mass budget in the various components, and the scaling relations between mass and luminosity are all consistent with a host of observational constraints. (Abridged)Comment: 12 pages, 7 figures, accepted for publication on the Astrophysical Journa

Convento di San Francesco a Folloni: the function of a Medieval Franciscan Friary seen through the burials

Background: The Franciscan Friary in Montella near Avellino in Southern Italy is of special interest because according to historical sources it was founded by St. Francis himself in AD 1221-1222. Human remains of several hundred individuals interred in the cloister walk have been unearthed during two excavation campaigns conducted in 2007-2008 and 2010. The environs of the friary have remained rural since the foundation preventing much modern contamination. The state of preservation of the skeletons is fair to good making a suite of analyses worthwhile. Results: The skeletons have been examined anthropologically and tissue samples have been subjected to radiocarbon dating, stable isotope measurements and trace element analyses by Inductively Coupled Plasma Mass Spectrometry and Cold Vapour Atomic Absorption Spectrometry. Conclusions: The radiocarbon dates are consistent with the historical sources and show that the cemetery in the cloister walk has been in uninterrupted use from the foundation of the friary in AD 1221-1222 and until the cemetery went out of use in AD 1524. The anthropological investigations show that the individuals interred at the friary would have been shorter than other Italians from the same time, and it seems that tuberculosis was more prevalent than leprosy. Isotopic measurements show a mixed agricultural and pastoral diet and none of the individuals were consuming marine protein. Based on the trace element analysis it seems that the people resided mainly at two distinct geographical areas, one of which was Montella. One individual stands out from the rest, because he was born and raised at some third geographical location distinct from Montella and because he sports the second oldest radiocarbon date of AD 1050-1249 (two sigma calibrated range). This date is consistent with the first generation of the founders of the friary-perhaps one of St. Francis' fellow travellers from Assisi

Correction to: Investigations of the relics and altar materials relating to the apostles St James and St Philip at the Basilica dei Santi XII Apostoli in Rome

Following publication of the original article [1], the authors identified an error in an author’s name. The incorrect name was: Erika Ribercini. The correct author name is: Erika Ribechini. The author group has been updated above and the original article [1] has been corrected

Structural Characterization of the P1+ Intermediate State of the P-Cluster of Nitrogenase

Nitrogenase is the enzyme that reduces atmospheric dinitrogen (N2) to ammonia (NH3) in biological systems. It catalyzes a series of single-electron transfers from the donor iron protein (Fe protein) to the molybdenum–iron protein (MoFe protein) that contains the iron–molybdenum cofactor (FeMo-co) sites where N2 is reduced to NH3. The P-cluster in the MoFe protein functions in nitrogenase catalysis as an intermediate electron carrier between the external electron donor, the Fe protein, and the FeMo-co sites of the MoFe protein. Previous work has revealed that the P-cluster undergoes redox-dependent structural changes and that the transition from the all-ferrous resting (PN) state to the two-electron oxidized P2+ state is accompanied by protein serine hydroxyl and backbone amide ligation to iron. In this work, the MoFe protein was poised at defined potentials with redox mediators in an electrochemical cell, and the three distinct structural states of the P-cluster (P2+, P1+, and PN) were characterized by X-ray crystallography and confirmed by computational analysis. These analyses revealed that the three oxidation states differ in coordination, implicating that the P1+ state retains the serine hydroxyl coordination but lacks the backbone amide coordination observed in the P2+ states. These results provide a complete picture of the redox-dependent ligand rearrangements of the three P-cluster redox states