Molecular dynamics study of hydrogen isotopes at the Be/BeO interface.

Molecular dynamics simulations are used to investigate the behaviour of D atoms at two interfaces between beryllium (Be) and beryllium oxide (BeO). After relaxation of the simulation cell, there are (a) localised defects at the interface and (b) a hexagonal misfit dislocation network creating a succession of compressed and expanded area from each side of the interface. The simulations between 750 K and 1500 K for tens to hundreds of nanoseconds show that both interfaces act as trapping sites for D atoms. The simulations also show that D atoms tend to migrate in the material where the hydrogen isotope solubility is the highest as predicted by thermodynamics. However, the simulations also shows that there are additional kinetic barriers (D trapping sites, D2formation/dissociation in BeO) that slow down the path to equilibrium. These additional kinetic barriers may influence the fuel retention and permeation in Be materials.

Molecular dynamics simulation of beryllium oxide irradiated by deuterium ions: sputtering and reflection.

The sputtering and reflection properties of wurtzite beryllium oxide (BeO) subjected to deuterium (D) ions bombardment at 300 K with ion energy between 10 eV and 200 eV is studied by classical molecular dynamics. Cumulative irradiations of wurtzite BeO show a D concentration threshold above which an 'unphysical dramatic' sputtering is observed. From the cumulative irradiations, simulation cells with different D concentrations are used to run non-cumulative irradiations at different concentrations. Using a D concentration close to the experimentally determined saturation concentration (0.12 atomic fraction), the simulations are able to reproduce accurately the experimental sputtering yield of BeO materials. The processes driving the sputtering of beryllium (Be) and oxygen (O) atoms as molecules are subsequently determined. At low irradiation energy, between 10 eV and 80 eV, swift chemical sputtering (SCS) is dominant and produces mostly OD z molecules. At high energy, the sputtered molecules are mostly Be x O y  molecules (mainly BeO dimer). Four different processes are associated to the formation of such molecules: the physical sputtering of BeO dimer, the delayed SCS not involving D ions and the detachment-induced sputtering. The physical sputtering of BeO dimer can be delayed if the sputtering event implies two interactions with the incoming ion (first interaction in its way in the material, the other in its way out if it is backscattered). The detachment-induced sputtering is a characteristic feature of the 'dramatic' sputtering and is mainly observed when the concentration of D is close to the threshold leading to this sputtering regime.

Hydrogen in beryllium oxide investigated by DFT: on the relative stability of charged-state atomic versus molecular hydrogen.

The behavior of hydrogen in perfect wurtzite beryllium oxide is herein investigated by means of electronic structure calculations based on density functional theory. The formation energies of the following set of states of hydrogen (H0, H+, H-, H2, [Formula: see text], [Formula: see text]) are computed and their solubility is established as a function of temperature and pressure with emphasis given to conditions relevant for hydrogen-implanted materials. It is found that all magnetic states H0, [Formula: see text], [Formula: see text] are unstable, while the relative stability of the non-magnetic states depends on the thermodynamic conditions: H2 prevails above temperatures around 900 K at standard pressure, which is the lowest temperature in experiments measuring the diffusion coefficient of hydrogen in wurtzite beryllium oxide. Under hydrogen implantation, the total concentration of hydrogen is fixed by the implantation source; it is found that molecular hydrogen prevails starting from a very low total concentration in hydrogen (as low as 10-40 at.fr.). Finally, the diffusion coefficient of H2 in beryllium oxide is calculated and the results are compared with previous experimental data.

Analytical bond order potential for simulations of BeO 1D and 2D nanostructures and plasma-surface interactions.

An analytical interatomic bond order potential for the Be-O system is presented. The potential is fitted and compared to a large database of bulk BeO and point defect properties obtained using density functional theory. Its main applications include simulations of plasma-surface interactions involving oxygen or oxide layers on beryllium, as well as simulations of BeO nanotubes and nanosheets. We apply the potential in a study of oxygen irradiation of Be surfaces, and observe the early stages of an oxide layer forming on the Be surface. Predicted thermal and elastic properties of BeO nanotubes and nanosheets are simulated and compared with published ab initio data.

In vitro activity of ceftobiprole on 440 Staphylococcus aureus strains isolated from bronchopulmonary infections.

OBJECTIVE: We assessed the in vitro activity of ceftobiprole on 440 Staphylococcus aureus clinical strains isolated from bronchopulmonary infections (2010-2014). METHODS: S. aureus isolates were characterized for methicillin resistance, PVL status, and clonal complex. All isolates were tested for minimal inhibitory concentrations (MIC) determination by broth microdilution method for ceftobiprole, ceftaroline fosamil, and comparator antibiotics (linezolid, tigecycline, vancomycin, and daptomycin). RESULTS: A total of 325 (74%) strains were methicillin-susceptible S. aureus (MSSA) and 115 (26%) were methicillin-resistant S. aureus (MRSA); 105 (24%) S. aureus strains were PVL-positive, including 35.2% (37/105) MRSA and 64.8% (68/105) MSSA. Ceftobiprole was highly active against S. aureus with MIC90 of 1 mg/L, MICs ranging between 0.12 and 4mg/L (only one resistant strain, MIC of 4 mg/L). MIC50 and MIC90 were twice lower in MSSA than MRSA. Moreover, PVL+ MRSA were slightly more susceptible to ceftobiprole (MIC50 of 0.5 mg/L and MIC90 of 1 mg/L) than PVL- MRSA (MIC50 and MIC90 of 1 mg/L). The ceftobiprole-resistant strain was also resistant to ceftaroline fosamil and presented the D239L mutation in PBP2A. The comparator antibiotics were equally active on the strains tested, with MIC90 of 0.5 mg/L for ceftaroline fosamil, tigecycline, and daptomycin; 1 mg/L for vancomycin; and 2 mg/L for linezolid. CONCLUSIONS: Our results suggest that ceftobiprole is highly active against S. aureus and is an effective alternative to vancomycin or linezolid in the management of staphylococcal pneumonia. However, close monitoring of isolates should be maintained to prevent resistant strain diffusion.

Superantigens and adhesins of infant gut commensal Staphylococcus aureus strains and association with subsequent development of atopic eczema.

BACKGROUND: According to the hygiene hypothesis, insufficient immune activation by microbes increases the risk of allergy development. Staphylococcus aureus, which is part of the skin and gut microbiota of infants in Western countries, produces a variety of T-cell-activating enterotoxins, called superantigens. OBJECTIVES: To investigate whether early (0-2 months of age) gut colonization by S. aureus strains that carry specific superantigens and adhesins was related to subsequent development of atopic eczema in a Swedish birth cohort. METHODS: Staphylococcus aureus was isolated from rectal swabs and cultured quantitatively from faecal samples, with individual strains being tested for carriage of genes for superantigens and adhesins. Atopic eczema was diagnosed at onset of symptoms and at 18 months of age. RESULTS: Although the frequency of early gut colonization by S. aureus was not related to subsequent eczema development, the S. aureus strains that were found to colonize those infants who developed atopic eczema were less likely to carry the gene encoding the superantigen SElM (P = 0·008) and the gene for elastin-binding protein (P = 0·03), compared with strains that were isolated from infants who had not developed atopic eczema by 18 months of age. CONCLUSIONS: Gut colonization by S. aureus strains carrying a certain combination of superantigen and adhesin genes was negatively associated with subsequent development of atopic eczema. Such strains may provide stimulation and promote maturation of the infant immune system.