2,739 research outputs found
Dislocation-mediated growth of bacterial cell walls
Recent experiments have illuminated a remarkable growth mechanism of
rod-shaped bacteria: proteins associated with cell wall extension move at
constant velocity in circles oriented approximately along the cell
circumference (Garner et al., Science (2011), Dominguez-Escobar et al. Science
(2011), van Teeffelen et al. PNAS (2011). We view these as dislocations in the
partially ordered peptidoglycan structure, activated by glycan strand extension
machinery, and study theoretically the dynamics of these interacting defects on
the surface of a cylinder. Generation and motion of these interacting defects
lead to surprising effects arising from the cylindrical geometry, with
important implications for growth. We also discuss how long range elastic
interactions and turgor pressure affect the dynamics of the fraction of
actively moving dislocations in the bacterial cell wall.Comment: to appear in PNA
Polycrystalline graphene and other two-dimensional materials
Graphene, a single atomic layer of graphitic carbon, has attracted intense
attention due to its extraordinary properties that make it a suitable material
for a wide range of technological applications. Large-area graphene films,
which are necessary for industrial applications, are typically polycrystalline,
that is, composed of single-crystalline grains of varying orientation joined by
grain boundaries. Here, we present a review of the large body of research
reported in the past few years on polycrystalline graphene. We discuss its
growth and formation, the microscopic structure of grain boundaries and their
relations to other types of topological defects such as dislocations. The
review further covers electronic transport, optical and mechanical properties
pertaining to the characterizations of grain boundaries, and applications of
polycrystalline graphene. We also discuss research, still in its infancy,
performed on other 2D materials such as transition metal dichalcogenides, and
offer perspectives for future directions of research.Comment: review article; part of focus issue "Graphene applications
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