A variety of organisms have evolved mechanisms to detect and respond to light, in which the response is mediated by protein structural changes after photon absorption. The initial step is often the ...photoisomerization of a conjugated chromophore. Isomerization occurs on ultrafast time scales and is substantially influenced by the chromophore environment. Here we identify structural changes associated with the earliest steps in the trans-to-cis isomerization of the chromophore in photoactive yellow protein. Femtosecond hard x-ray pulses emitted by the Linac Coherent Light Source were used to conduct time-resolved serial femtosecond crystallography on photoactive yellow protein microcrystals over a time range from 100 femtoseconds to 3 picoseconds to determine the structural dynamics of the photoisomerization reaction.
Scaling the Si MOSFET is reconsidered. Requirements on subthreshold leakage control force conventional scaling to use high doping as the device dimension penetrates into the deep-submicrometer ...regime, leading to an undesirably large junction capacitance and degraded mobility. By studying the scaling of fully depleted SOI devices, the important concept of controlling horizontal leakage through vertical structures is highlighted. Several structural variations of conventional SOI structures are discussed in terms of a natural length scale to guide the design. The concept of vertical doping engineering can also be realized in bulk Si to obtain good subthreshold characteristics without large junction capacitance or heavy channel doping.< >
We describe a new generation of algorithms capable of mapping the structure and conformations of macromolecules and their complexes from large ensembles of heterogeneous snapshots, and demonstrate ...the feasibility of determining both discrete and continuous macromolecular conformational spectra. These algorithms naturally incorporate conformational heterogeneity without resort to sorting and classification, or prior knowledge of the type of heterogeneity present. They are applicable to single-particle diffraction and image datasets produced by X-ray lasers and cryo-electron microscopy, respectively, and particularly suitable for systems not easily amenable to purification or crystallization.
Single-particle structure and dynamics Ourmazd, A.
Acta crystallographica. Section A, Foundations of crystallography,
08/2013, Letnik:
69, Številka:
a1
Journal Article
We describe how lattice images may be used to measure the variation of the projected potential in crystalline solids in any projection, with no knowledge of the imaging conditions. This approach is ...applicable to many solids with atoms residing entirely on coherent lattices, in which interfacial topography or changes in composition are of interest. We present atomic-level topographic maps of Si/SiO
2 interfaces in plan-view, and compositional maps of Si/GeSi/Si quantum wells in cross-section. We conclude with a detailed discussion of the capabilities and limitations of this approach.
Chemical lattice imaging is combined with digital pattern recognition to map, at near-atomic resolution, the compositional change across GaAs/AlGaAs interfaces of the highest optical quality. These ...maps quantify the information content of each unit cell of the lattice image. Results show that state-of-art GaAs /AlGaAs interfaces contain substantial atomic roughness on scales finer than suggested by optical measurements. (Author)
PDF
