Crystallographic structure reveals phosphorylated pilin from Neisseria : phosphoserine sites modify type IV pilus surface chemistry and fibre morphology

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72468/1/j.1365-2958.1999.01184.x.pd

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

The influence of a material microstructure on the behaviour of dopants

Dopants, when introduced into a host lattice, can influence profoundly the properties of a material. It is therefore desirable in the design of new materials with improved or indeed optimised properties to understand the behaviour of such dopants. Most previous simulations have explored the structure and segregation of dopants in a 'perfect' host lattice, or, more recently, within a host lattice comprising a single additional structural feature such as a vacancy or dislocation. However, real materials are likely to comprise a complex microstructure. Here, we present simulations which explore the behaviour and segregation of dopant ions within a material which comprises such a complex microstructure. Specifically, we consider Ca-doped SrO thin films supported on MgO. Microstructural features of the host SrO lattice include: heterointerfaces, dislocation networks, defects (vacancies, substitutionals, and interstitials) and defect clusters, interfacial and epitaxial configurations, low interfacial densities, surface structures and morphologies. Our simulations suggest that the dopant Ca ions segregate to the surface of the SrO thin film, accommodate lattice positions within dislocation cores and migrate across the SrO/MgO heterointerfacial boundary. Such models can then be used as realistic starting configurations to calculate pertinent physical properties as performed previously ('Synthesis, structure and ionic conductivity in nanopolycrystalline BaF2/CaF2 heterolayers': D.C. Sayle et al., Chem. Commun., 2003, 1804 [ref. 11]). The strategy provides therefore a framework for using simulation techniques predictively to design systems with tailored properties

Atomistic structure of oxide nanoparticles supported on an oxide substrate

The atomistic structures of SrO (15×15×2.2nm), CaO (14×14×2nm), and MgO (12×12×2nm) nanoparticles, supported on BaO(001) and synthesized using a simulated amorphization and recrystallization strategy, are presented. The SrO and CaO exhibit cubic “slab” morphologies in contrast to the MgO nanoparticle, which comprises various misaligned interconnecting crystallites. The lattice misfit was found to have a profound influence on the structure of the nanoparticles. The SrO nanoparticle (-7% misfit) was found to lie coherent with respect to the substrate across the entire area covered by the SrO. Conversely, only small regions of the CaO were found to be coherent with the BaO substrate (-15% misfit), with screw-edge dislocations located at regions where the ions became misaligned. The MgO nanoparticle (-31% misfit) exhibited no regions of coherence with respect to the underlying BaO substrate. Defects (vacancies and substitutionals) and defect clusters including voids were also identified for each system and act to help reduce locally the lattice misfit thereby enhancing the stability. Specifically, the results indicate that as the lattice misfit associated with the system increases, so the interfacial layer of the substrate becomes more defective. Arguments, based on the results of the study, are presented, which suggest that the area of the nanoparticle in contact with the substrate is linked with the critical thickness to dislocation evolution for a particular system. That the limitations of periodic boundary conditions can be eliminated when simulating nanoparticles compared with thin films, which cover completely the substrate material, is discussed

Synthesis, structure and ionic conductivity in nanopolycrystalline BaF2/CaF2 heterolayers

Atomistic simulations have shown that the calculated conductivity of nano-polycrystalline BaF2/CaF2 heterolayers is considerably higher than the component bulk materials and we predict that grain-boundary diffusion is the key to fast ionic conductivity in these systems

Metal oxide encapsulated nanoparticles

Atomistic computer simulation techniques have been employed to generate a model for a 25 nm3 CaO nanoparticle, encapsulated within the near surface region of an MgO lattice. We find that the 'internal' morphology of the resulting encapsulated CaO nanoparticle is 'pseudo-spherical' and exhibits {100}, {110} and {111} facets. The encapsulated nanoparticle suffers significant structural changes in comparison to the bulk parent oxide: Regions within the CaO nanoparticle are identified to suffer both tension and compression together with plane curvature. In addition a wealth of defects (isolated vacancies, interstitials and substitutionals including complex clustering) evolve within the near (1-2 atomic planes) interracial regions of the CaO nanoparticle and surrounding MgO lattice. The CaO nanoparticle is observed to lie epitaxially with respect to the host MgO lattice with CaO{100} and MgO{100} planes aligned; dislocations evolve to accommodate the +13% bulk lattice misfit associated with the system, the core structures of which are localised at regions of poor registry between the {100} planes. The CaO nanoparticle is observed to rotate by about 6° with respect to the encapsulating MgO matrix, which results in some anisotropy in structure. Comprehensive depictions of the atomistic structure and morphology of the encapsulated CaO nanoparticle and surrounding MgO lattice are presented using molecular graphical techniques

Computer aided design of nano-structured materials with tailored ionic conductivities

We show, using simulation techniques, that the high ionic conductivity in BaF2/CaF2 heterolayers is because the interfaces reduce the activation energy barriers to mobility and increase the number of charge carriers