Mapping deuterated methanol toward L1544: I. Deuterium fraction and comparison with modeling

The study of deuteration in pre-stellar cores is important to understand the physical and chemical initial conditions in the process of star formation. In particular, observations toward pre-stellar cores of methanol and deuterated methanol, solely formed on the surface of dust grains, may provide useful insights on surface processes at low temperatures. Here we analyze maps of CO, methanol, formaldehyde and their deuterated isotopologues toward a well-known pre-stellar core. This study allows us to test current gas-dust chemical models. Single-dish observations of CH$_3$OH, CH$_2$DOH, H$_2$CO, H_2\,^{13}CO, HDCO, D$_2$CO and C$^{17}$O toward the prototypical pre-stellar core L1544 were performed at the IRAM 30 m telescope. We analyze their column densities, distributions, and compare these observations with gas-grain chemical models. The maximum deuterium fraction derived for methanol is [CH$_2$DOH]/[CH$_3$OH] $\sim$ 0.08$\pm$0.02, while the measured deuterium fractions of formaldehyde at the dust peak are [HDCO]/[H$_2$CO] $\sim$ 0.03$\pm$0.02, [D$_2$CO]/[H$_2$CO] $\sim$ 0.04$\pm$0.03 and [D$_2$CO]/[HDCO] $\sim$ 1.2$\pm$0.3. Observations differ significantly from the predictions of models, finding discrepancies between a factor of 10 and a factor of 100 in most cases. It is clear though that to efficiently produce methanol on the surface of dust grains, quantum tunneling diffusion of H atoms must be switched on. It also appears that the currently adopted reactive desorption efficiency of methanol is overestimated and/or that abstraction reactions play an important role. More laboratory work is needed to shed light on the chemistry of methanol, an important precursor of complex organic molecules in space.Comment: Accepted for publication in A&

Partitioning of plant functional trait variation into phenotypic plasticity and neutral components reveals functional differences among neotropical tree species

Background: Tropical plant communities exhibit extraordinary species richness and functional diversity in highly heterogeneous environments. Albeit the fact that such environmental filtering shapes local species composition and associated plant functional traits, it remains elusive to what extend tropical vegetation might be able to acclimate to environmental changes via phenotypic plasticity, which could be a critical determinant affecting the resistance and resilience of tropical vegetation to projected climate change. Methods: Based on a dataset compiled from 345 individuals and comprising 34 tropical tree species we here investigated the role of phenotypic plasticity versus non-plastic variation among key plant functional traits, i.e. wood density, maximum height, leaf thickness, leaf area, specific leaf area, leaf dry mass, nitrogen and phosphorus content. We hypothesized that trait variation due to plasticity is driven by environmental variability independently of spatial effects due to geographic distance between forest stands, whereas non-plastic variation increases with geographic distance due to adaption of the plant community to the local environment. Based on these hypotheses we partitioned total observed trait variation into phenotypic plasticity and neutral components and quantified respective amount of variation related to environmental filtering and neutral community assembly. Results: We found that trait variation was strongly related to spatial factors, thus often masking phenotypic plasticity in response to environmental cues. However, respective environmental factors differed among plant functional traits, such that leaf traits varied in association with light regime and soil nutrient content, whereas wood traits were related to topography and soil water content. Our results further suggest that phenotypic plasticity increased with the range size of congeneric tree species, indicating less plasticity within range restricted endemics compared to their widespread congeners. Conclusions: Differences in phenotypic trait plasticity affect stress tolerance and range size of tropical tree species, therefore endemic species could be especially prone to projected climate change

Reciprocal space mapping of magnetic order in thick epitaxial MnSi films

We report grazing incidence small angle neutron scattering (GISANS) and complementary off-specular neutron reflectometry (OSR) of the magnetic order in a single-crystalline epitaxial MnSi film on Si(111) in the thick film limit. Providing a means of direct reciprocal space mapping, GISANS and OSR reveal a magnetic modulation perpendicular to the films under magnetic fields parallel and perpendicular to the film, where additional polarized neutron reflectometry (PNR) and magnetization measurements are in excellent agreement with the literature. Regardless of field orientation, our data does not suggest the presence of more complex spin textures, notably the formation of skyrmions. This observation establishes a distinct difference with bulk samples of MnSi of similar thickness under perpendicular field, in which a skyrmion lattice dominates the phase diagram. Extended x-ray absorption fine structure measurements suggest that small shifts of the Si positions within the unstrained unit cell control the magnetic state, representing the main difference between the films and thin bulk samples

Bacteriostatic and bactericide action of drugs from condensation of sulfanilamide with formaldehyde

O artigo não apresenta resumo.The article has no abstract

Microscopic Surface Structure of Liquid Alkali Metals

We report an x-ray scattering study of the microscopic structure of the surface of a liquid alkali metal. The bulk liquid structure factor of the eutectic K67Na33 alloy is characteristic of an ideal mixture, and so shares the properties of an elemental liquid alkali metal. Analysis of off-specular diffuse scattering and specular x-ray reflectivity shows that the surface roughness of the K-Na alloy follows simple capillary wave behavior with a surface structure factor indicative of surface induced layering. Comparison of thelow-angle tail of the K67Na33 surface structure factor with the one measured for liquid Ga and In previously suggests that layering is less pronounced in alkali metals. Controlled exposure of the liquid to H2 and O2 gas does not affect the surface structure, indicating that oxide and hydride are not stable at the liquid surface under these experimental conditions.Comment: 12 pages, 3 figures, published in Phys. Rev.

Grain Boundaries in Graphene on SiC(0001ˉ\bar{1}) Substrate

Grain boundaries in epitaxial graphene on the SiC(000$\bar{1}$) substrate are studied using scanning tunneling microscopy and spectroscopy. All investigated small-angle grain boundaries show pronounced out-of-plane buckling induced by the strain fields of constituent dislocations. The ensemble of observations allows to determine the critical misorientation angle of buckling transition $\theta_c = 19 \pm~2^\circ$. Periodic structures are found among the flat large-angle grain boundaries. In particular, the observed $\theta = 33\pm2^\circ$ highly ordered grain boundary is assigned to the previously proposed lowest formation energy structural motif composed of a continuous chain of edge-sharing alternating pentagons and heptagons. This periodic grain boundary defect is predicted to exhibit strong valley filtering of charge carriers thus promising the practical realization of all-electric valleytronic devices

Growth hormone inhibits hepatic de novo lipogenesis in adult mice

Patients with nonalcoholic fatty liver disease (NAFLD) are reported to have low growth hormone (GH) production and/or hepatic GH resistance. GH replacement can resolve the fatty liver condition in diet-induced obese rodents and in GH-deficient patients. However, it remains to be determined whether this inhibitory action of GH is due to direct regulation of hepatic lipid metabolism. Therefore, an adult-onset, hepatocyte-specific, GH receptor (GHR) knockdown (aLivGHRkd) mouse was developed to model hepatic GH resistance in humans that may occur after sexual maturation. Just 7 days after aLivGHRkd, hepatic de novo lipogenesis (DNL) was increased in male and female chow-fed mice, compared with GHR-intact littermate controls. However, hepatosteatosis developed only in male and ovariectomized female aLivGHRkd mice. The increase in DNL observed in aLivGHRkd mice was not associated with hyperactivation of the pathway by which insulin is classically considered to regulate DNL. However, glucokinase mRNA and protein levels as well as fructose-2,6-bisphosphate levels were increased in aLivGHRkd mice, suggesting that enhanced glycolysis drives DNL in the GH-resistant liver. These results demonstrate that hepatic GH actions normally serve to inhibit DNL, where loss of this inhibitory signal may explain, in part, the inappropriate increase in hepatic DNL observed in NAFLD patients