243 research outputs found
The native architecture of a photosynthetic membrane
In photosynthesis, the harvesting of solar energy and its subsequent conversion into a stable charge separation are dependent upon an interconnected macromolecular network of membrane-associated chlorophyll–protein complexes. Although the detailed structure of each complex has been determined, the size and organization of this network are unknown. Here we show the use of atomic force microscopy to directly reveal a native bacterial photosynthetic membrane. This first view of any multi-component membrane shows the relative positions and associations of the photosynthetic complexes and reveals crucial new features of the organization of the network: we found that the membrane is divided into specialized domains each with a different network organization and in which one type of complex predominates. Two types of organization were found for the peripheral light-harvesting LH2 complex. In the first, groups of 10–20 molecules of LH2 form light-capture domains that interconnect linear arrays of dimers of core reaction centre (RC)–light-harvesting 1 (RC–LH1–PufX) complexes; in the second they were found outside these arrays in larger clusters. The LH1 complex is ideally positioned to function as an energy collection hub, temporarily storing it before transfer to the RC where photochemistry occurs: the elegant economy of the photosynthetic membrane is demonstrated by the close packing of these linear arrays, which are often only separated by narrow 'energy conduits' of LH2 just two or three complexes wide
Paediatric tube-feeding: An agenda for care improvement and research.
This article presents an agenda to improve the care and wellbeing of children with paediatric feeding disorder who require tube feeding (PFD-T). PFD-T requires urgent attention in practice and research. Priorities include: routine collection of PFD-T data in health-care records; addressing the tube-feeding lifecycle; and reducing the severity and duration of disruption caused by PFD-T where possible. This work should be underpinned by principles of involving, respecting and connecting families
Stratified spatiotemporal chaos in anisotropic reaction-diffusion systems
Numerical simulations of two dimensional pattern formation in an anisotropic
bistable reaction-diffusion medium reveal a new dynamical state, stratified
spatiotemporal chaos, characterized by strong correlations along one of the
principal axes. Equations that describe the dependence of front motion on the
angle illustrate the mechanism leading to stratified chaos
Selection for Replicases in Protocells
PMCID: PMC3649988This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Flexibility and size heterogeneity of the LH1 light harvesting complex revealed by atomic force microscopy - Functional significance for bacterial photosynthesis
Previous electron microscopic studies of bacterial RC-LH1 complexes demonstrated both circular and elliptical conformations of the LH1 ring, and this implied flexibility has been suggested to allow passage of quinol from the
Non-thermal response of YBCO thin films to picosecond THz pulses
The photoresponse of YBa2Cu3O7-d thin film microbridges with thicknesses
between 15 and 50 nm was studied in the optical and terahertz frequency range.
The voltage transients in response to short radiation pulses were recorded in
real time with a resolution of a few tens of picoseconds. The bridges were
excited by either femtosecond pulses at a wavelength of 0.8 \mu m or broadband
(0.1 - 1.5 THz) picosecond pulses of coherent synchrotron radiation. The
transients in response to optical radiation are qualitatively well explained in
the framework of the two-temperature model with a fast component in the
picosecond range and a bolometric nanosecond component whose decay time depends
on the film thickness. The transients in the THz regime showed no bolometric
component and had amplitudes up to three orders of magnitude larger than the
two-temperature model predicts. Additionally THz-field dependent transients in
the absence of DC bias were observed. We attribute the response in the THz
regime to a rearrangement of vortices caused by high-frequency currents
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