Showing papers by "Uwe Weierstall published in 2008"
TL;DR: In this article, a single-file stream of droplets of a fluid to a high-vacuum system was produced by using a two concentric tubes with a smoothly converging-diverging exit channel and the outlet end positioned within the converging section of the exit channel.
Abstract: A nozzle for producing a single-file stream of droplets of a fluid, methods using the nozzle, and an injector, comprising the nozzle of the invention, for providing the single-file stream of droplets of a fluid to a high-vacuum system are described. The nozzle comprises two concentric tubes wherein the outer tube comprises a smoothly converging-diverging exit channel and the outlet end of the first tube is positioned within the converging section of the exit channel.
410 citations
TL;DR: In this article, a droplet beam source based on the gas-dynamic forces exerted by a co-flowing gas was proposed to avoid the need for a solid nozzle to form a microscopic liquid jet and alleviate the clogging problems that plague conventional droplet sources of small diameter.
Abstract: As shown by Ganan-Calvo and co-workers, a free liquid jet can be compressed in iameter through gas-dynamic forces exerted by a co-flowing gas, obviating the need for a solid nozzle to form a microscopic liquid jet and thereby alleviating the clogging problems that plague conventional droplet sources of small diameter. We describe in this paper a novel form of droplet beam source based on this principle. The source is miniature, robust, dependable, easily fabricated, and eminently suitable for delivery of microscopic liquid droplets, including hydrated biological samples, into vacuum for analysis using vacuum instrumentation. Monodisperse, single file droplet streams are generated by triggering the device with a piezoelectric actuator. The device is essentially immune to clogging.
367 citations
TL;DR: Finite-element analysis from the structure of the labrynthine internal structure of a tantalum oxide nanofoam reveals mechanical properties consistent with bulk samples and with a diffusion-limited cluster aggregation model, while excess mass on the nodes discounts the dangling fragments hypothesis of percolation theory.
Abstract: Ultralow density polymers, metals, and ceramic nanofoams are valued for their high strength-to-weight ratio, high surface area, and insulating properties ascribed to their structural geometry. We obtain the labrynthine internal structure of a tantalum oxide nanofoam by x-ray diffractive imaging. Finite-element analysis from the structure reveals mechanical properties consistent with bulk samples and with a diffusion-limited cluster aggregation model, while excess mass on the nodes discounts the dangling fragments hypothesis of percolation theory.
107 citations
TL;DR: In this article, a comparison of conventional Rayleigh sources and electrospray-assisted Rayleigh source for serial diffraction of proteins is made and conclusions drawn on the basis of time-resolved optical images of the droplet streams produced by these sources.
Abstract: Serial diffraction of proteins requires an injection method to deliver analyte molecules—preferably uncharged, fully hydrated, spatially oriented, and with high flux—into a focused probe beam of electrons or X-rays that is only a few tens of microns in diameter. This work examines conventional Rayleigh sources and electrospray-assisted Rayleigh sources as to their suitability for this task. A comparison is made and conclusions drawn on the basis of time-resolved optical images of the droplet streams produced by these sources. Straight-line periodic streams of monodisperse droplets were generated with both sources, achieving droplet diameters of 4 and 1 micrometer, respectively, for the conventional and electrospray-assisted versions. Shrinkage of droplets by evaporation is discussed and quantified. It is shown experimentally that proteins pass undamaged through a conventional Rayleigh droplet source.
71 citations
TL;DR: The first powder diffraction patterns from a membrane protein, photosystem I, with crystallite sizes of less than 500 nm are presented, and these preliminary patterns show the lowest-order reflections, which agree quantitatively with theoretical calculations of the powder profile.
Abstract: Atomic-resolution structures from small proteins have recently been determined from high-quality powder diffraction patterns using a combination of stereochemical restraints and Rietveld refinement [Von Dreele (2007), J. Appl. Cryst. 40, 133–143; Margiolaki et al. (2007), J. Am. Chem. Soc. 129, 11865–11871]. While powder diffraction data have been obtained from batch samples of small crystal-suspensions, which are exposed to X-rays for long periods of time and undergo significant radiation damage, the proof-of-concept that protein powder diffraction data from nanocrystals of a membrane protein can be obtained using a continuous microjet is shown. This flow-focusing aerojet has been developed to deliver a solution of hydrated protein nanocrystals to an X-ray beam for diffraction analysis. This method requires neither the crushing of larger polycrystalline samples nor any techniques to avoid radiation damage such as cryocooling. Apparatus to record protein powder diffraction in this manner has been commissioned, and in this paper the first powder diffraction patterns from a membrane protein, photosystem I, with crystallite sizes of less than 500 nm are presented. These preliminary patterns show the lowest-order reflections, which agree quantitatively with theoretical calculations of the powder profile. The results also serve to test our aerojet injector system, with future application to femtosecond diffraction in free-electron X-ray laser schemes, and for serial crystallography using a single-file beam of aligned hydrated molecules.
53 citations
TL;DR: It is found that multiple single-file protein beams will be needed for sub-nanometer resolution on current third-generation synchrotrons, but not on fourth-generation designs, where reconstruction of secondary protein structure at a resolution of 7 A should be possible with relatively short exposures.
Abstract: The resolution of X-ray diffraction microscopy is limited by the maximum dose that can be delivered prior to sample damage. In the proposed serial crystallography method, the damage problem is addressed by distributing the total dose over many identical hydrated macromolecules running continuously in a single-file train across a continuous X-ray beam, and resolution is then limited only by the available molecular and X-ray fluxes and molecular alignment. Orientation of the diffracting molecules is achieved by laser alignment. The incident X-ray fluence (energy/area) is evaluated that is required to obtain a given resolution from (i) an analytical model, giving the count rate at the maximum scattering angle for a model protein, (ii) explicit simulation of diffraction patterns for a GroEL–GroES protein complex, and (iii) the spatial frequency cut-off of the transfer function following iterative solution of the phase problem, and reconstruction of an electron density map in the projection approximation. These calculations include counting shot noise and multiple starts of the phasing algorithm. The results indicate counting time and the number of proteins needed within the beam at any instant for a given resolution and X-ray flux. An inverse fourth-power dependence of exposure time on resolution is confirmed, with important implications for all coherent X-ray imaging. It is found that multiple single-file protein beams will be needed for sub-nanometer resolution on current third-generation synchrotrons, but not on fourth-generation designs, where reconstruction of secondary protein structure at a resolution of 7 A should be possible with relatively short exposures.
47 citations
TL;DR: It is shown that the principal axes of a compact charge-density distribution can be obtained from projections of its autocorrelation function, which is directly accessible in diffraction experiments.
Abstract: A method is proposed for obtaining three simultaneous projections of a target from a single radiation pulse, which also allows the relative orientation of successive targets to be determined. The method has application to femtosecond x-ray diffraction, and does not require solution of the phase problem. We show that the principal axes of a compact charge-density distribution can be obtained from projections of its autocorrelation function, which is directly accessible in diffraction experiments. The results may have more general application to time resolved tomographic pump-probe experiments and time-series imaging.
31 citations