Stacking Domains and Dislocation Networks in Marginally Twisted Bilayers of Transition Metal Dichalcogenides.

We apply a multiscale modeling approach to study lattice reconstruction in marginally twisted bilayers of transition metal dichalcogenides (TMD). For this, we develop density functional theory parametrized interpolation formulae for interlayer adhesion energies of MoSe_{2}, WSe_{2}, MoS_{2}, and WS_{2}, combine those with elasticity theory, and analyze the bilayer lattice relaxation into mesoscale domain structures. Paying particular attention to the inversion asymmetry of TMD monolayers, we show that 3R and 2H stacking domains, separated by a network of dislocations develop for twist angles θ^{∘}<θ_{P}^{∘}∼2.5° and θ^{∘}<θ_{AP}^{∘}∼1° for, respectively, bilayers with parallel (P) and antiparallel (AP) orientation of the monolayer unit cells and suggest how the domain structures would manifest itself in local probe scanning of marginally twisted P and AP bilayers.

The preterm gut microbiota: changes associated with necrotizing enterocolitis and infection.

AIM: To describe gut colonization in preterm infants using standard culture and 16S gene rRNA profiling, exploring differences in healthy infants and those who developed NEC/late onset sepsis (LOS). METHODS: Ninety-nine stools from 38 infants of median 27-week gestation were cultured; 44 stools from 27 infants had their microbial profiles determined by 16S. Ordination analyses explored effects of patient variables on gut communities. RESULTS: Standard microbiological culture identified a mean of two organisms (range 0-7), DGGE 12 (range 3-18) per patient. Enterococcus faecalis and coagulase negative staphylococci (CONS) were most common by culture (40% and 39% of specimens). Meconium was not sterile. No fungi were cultured. Bacterial community structures in infants with NEC and LOS differed from healthy infants. Infants who developed NEC carried more CONS (45% vs 30%) and less Enterococcus faecalis (31% vs 57%). 16S identified Enterobacter and Staphylococcus presence associated with NEC/LOS, respectively. CONCLUSIONS: Important differences were found in the gut microbiota of preterm infants who develop NEC/LOS. The relationship of these changes to current practices in neonatal intensive care requires further exploration.