Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapor Deposition

The strong interest in graphene has motivated the scalable production of high quality graphene and graphene devices. Since large-scale graphene films synthesized to date are typically polycrystalline, it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycrystalline Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman "D" peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.Comment: New version with additional data. Accepted by Nature Material

Transcriptional Regulator PerA Influences Biofilm-Associated, Platelet Binding, and Metabolic Gene Expression in Enterococcus faecalis

Enterococcus faecalis is an opportunistic pathogen and a leading cause of nosocomial infections, traits facilitated by the ability to quickly acquire and transfer virulence determinants. A 150 kb pathogenicity island (PAI) comprised of genes contributing to virulence is found in many enterococcal isolates and is known to undergo horizontal transfer. We have shown that the PAI-encoded transcriptional regulator PerA contributes to pathogenicity in the mouse peritonitis infection model. In this study, we used whole-genome microarrays to determine the PerA regulon. The PerA regulon is extensive, as transcriptional analysis showed 151 differentially regulated genes. Our findings reveal that PerA coordinately regulates genes important for metabolism, amino acid degradation, and pathogenicity. Further transcriptional analysis revealed that PerA is influenced by bicarbonate. Additionally, PerA influences the ability of E. faecalis to bind to human platelets. Our results suggest that PerA is a global transcriptional regulator that coordinately regulates genes responsible for enterococcal pathogenicity

Anti-angiogenic therapy for cancer: Current progress, unresolved questions and future directions

Tumours require a vascular supply to grow and can achieve this via the expression of pro-angiogenic growth factors, including members of the vascular endothelial growth factor (VEGF) family of ligands. Since one or more of the VEGF ligand family is overexpressed in most solid cancers, there was great optimism that inhibition of the VEGF pathway would represent an effective anti-angiogenic therapy for most tumour types. Encouragingly, VEGF pathway targeted drugs such as bevacizumab, sunitinib and aflibercept have shown activity in certain settings. However, inhibition of VEGF signalling is not effective in all cancers, prompting the need to further understand how the vasculature can be effectively targeted in tumours. Here we present a succinct review of the progress with VEGF-targeted therapy and the unresolved questions that exist in the field: including its use in different disease stages (metastatic, adjuvant, neoadjuvant), interactions with chemotherapy, duration and scheduling of therapy, potential predictive biomarkers and proposed mechanisms of resistance, including paradoxical effects such as enhanced tumour aggressiveness. In terms of future directions, we discuss the need to delineate further the complexities of tumour vascularisation if we are to develop more effective and personalised anti-angiogenic therapies. © 2014 The Author(s)

Estuarine processes modify the isotope composition of dissolved riverine barium fluxes to the ocean

Barium (Ba) isotope variations offer the potential to trace environmental processes, including long-term changes in river discharge and marine export production. Riverine inputs are an important source of dissolved Ba to the ocean, which we estimate to be ~10 to 20 Gmol yr&minus;1. A large fraction (~20 to 75%) of this net riverine dissolved Ba flux to the ocean is derived from estuarine processes, in particular the release of exchangeable Ba from riverine suspended particles due to exchange with major cations in seawater. Despite the importance of this process for controlling the input of dissolved Ba to the ocean, its impact on the &delta;138/134Ba of net riverine dissolved Ba fluxes remains unknown. To address this observational gap, Ba concentration and isotope data from across the estuarine mixing zones of the Amazon (Brazil), Fly (Papua New Guinea) and Johor (Malaysia) Rivers are presented. Desorption from suspended riverine particles releases Ba with &delta;138/134Ba 0.2 to 0.3&permil; lower than corresponding river dissolved loads, modifying the isotope composition of net riverine dissolved Ba fluxes that reach the ocean. This offset likely represents an isotope fractionation accompanying the adsorption of Ba by particulate phases within river catchments, which can explain the systematic enrichment of heavier Ba isotopes in river dissolved loads relative to weathering lithologies. River dissolved loads are also systematically offset to higher &delta;138/134Ba than the main oceanic Ba sink: burial of BaSO4&nbsp;in&nbsp;marine sediment. This represents an apparent imbalance in the modern marine Ba isotope budget. Our results suggest that accounting for modification of the &delta;138/134Ba of net riverine Ba fluxes to the ocean by estuarine processes is likely to play a key role towards balancing the modern marine Ba isotope budget.</p