6,436 research outputs found
Thermal fluctuations and stability of solid-supported lipid membranes
No full textIn this review article we discuss recent work on the thermal stability, thermal fluctuations and interaction forces in lipid membrane stacks. The lipid bilayers are deposited on solid surfaces for investigation by interface sensitive x-ray and neutron scattering on length scales ranging from the molecular to the mesoscopic scale. We discuss how the structure, composition, fluctuations, and interactions in lipid and biomimetic membranes can be studied in the fluid Lalpha phase. Results on the interaction potentials, height-height correlation functions, elasticity parameters, fluid lipid chain ordering, and collective lipid chain motions are discussed
Lipid–peptide interaction in oriented bilayers probed by interface-sensitive scattering methods
No full textOriented lipid membranes deposited on solid substrates offer unique experimental opportunities to study lipid bilayer structure and lipid-peptide interaction in suitable model systems. In particular, modern interface-sensitive X-ray and neutron scattering methods can be used to probe the short-range order and molecular conformations of peptides and lipids in the fluid state of the bilayer
Structure and fluctuations of highly oriented phospholipid membranes
No full textHighly oriented lipid membranes deposited on solid substrates offer unique experimental possibilities to study self-assembly phenomena, fluctuations, and interactions in lipid bilayer systems, both with and without additional membrane-active molecules such as amphiphilic peptides or membrane proteins. In diffraction experiments, the high orientation allows for a precise distinction between the normal q(z), and lateral component q(parallel to) of the scattering vector (q) over right arrow, opening up a way to study biologically relevant questions associated with the lateral structure of the bilayers. Modern sources and instruments for neutron and X-ray scattering, in particular the advent of third-generation synchrotron sources enable studies even of weakly scattering and weakly ordered systems. (C) 2000 Elsevier Science Ltd. All rights reserved
Finite difference methods for stationary and time-dependent X-ray propagation
No full textWe have generalized finite-difference (FD) simulations for time-dependent field propagation problems, in particular in view of ultra-short x-ray pulse propagation and dispersion. To this end, we first derive the stationary paraxial (parabolic) wave equation for the scalar field envelope in a more general manner than typically found in the literature. We then present an efficient FD implementation of propagators for different dimensionality for stationary field propagation, before we treat time-dependent problems by spectral decomposition, and suitable numerical sampling. We prove the validity of the numerical approach by comparison to analytical theory, using simple tractable propagation problems. Finally, we apply the framework to the problem of modal dispersion in X-ray waveguide. We show that X-ray waveguides can be considered as non-dispersive optical elements down to sub-femtosecond pulse width. Only when considering resonant absorption close to an X-ray absorption edge, we observe pronounced dispersion effects for experimentally achievable pulse widths. All code used for the work is made available as supplemental material.Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/50110000165
Coherence-resolution relationship in holographic and coherent diffractive imaging
No full textWe study by numerical simulation how spatial coherence affects the reconstruction quality of images in coherent diffractive x-ray imaging. Using a conceptually simple, but computationally demanding approach, we have simulated diffraction data recorded under partial coherence, and then use the data for iterative reconstruction algorithms using a support constraint. By comparison of experimental regimes and parameters, we observe a significantly higher robustness against partially coherent illumination in the near-field compared to the far-field setting.Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/50110000165
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