Showing papers by "Uwe Weierstall published in 2004"
TL;DR: The Shannon sampling, defined by the transform of the periodically repeated autocorrelation of the object, is related to Bragg scattering from an equivalent crystal, and shown to be consistent with the sampling of Young's fringes established by scattering from extreme points in the object.
123 citations
TL;DR: An iterative phase retrieval method for nonperiodic objects has been developed from the charge-flipping algorithm proposed in crystallography and a combination of the hybrid input-output (HIO) algorithm and the flipping algorithm has greatly improved performance.
Abstract: An iterative phase retrieval method for nonperiodic objects has been developed from the charge-flipping algorithm proposed in crystallography. A combination of the hybrid input-output (HIO) algorithm and the flipping algorithm has greatly improved performance. In this combined algorithm the flipping algorithm serves to find the support (object boundary) dynamically, and the HIO part improves convergence and moves the algorithm out of local minima. It starts with a single intensity measurement in the Fourier domain and does not require a priori knowledge of the support in the image domain. This method is suitable for general image recovery from oversampled diffuse elastic x-ray and electron-diffraction intensities. The relationship between this algorithm and the output-output algorithm is elucidated.
42 citations
TL;DR: In this paper, the use of one or more gold nanoballs as reference objects for Fourier transform holography (FTH) was analyzed using experimental soft x-ray diffraction from objects consisting of separated clusters of these balls.
Abstract: The use of one or more gold nanoballs as reference objects for Fourier transform holography (FTH) is analyzed using experimental soft x-ray diffraction from objects consisting of separated clusters of these balls. The holograms are deconvoluted against ball reference objects to invert to images, in combination with a Wiener filter to control noise. A resolution of ∼30nm, smaller than one ball, is obtained even if a large cluster of balls is used as the reference, giving the best resolution yet obtained by x-ray FTH. Methods of dealing with missing data due to a beamstop are discussed. Practical prepared objects which satisfy the FTH condition are suggested, and methods of forming them described.
39 citations
TL;DR: The theoretical basis for the reconstruction algorithm, its implementation, and quantitative results of tests on synthetic and experimentally obtained data are described.
Abstract: Speden is a computer program that reconstructs the electron density of single particles from their x-ray diffraction patterns, using a single-particle adaptation of the Holographic Method in crystallography. (Szoke, A., Szoke, H., and Somoza, J.R., 1997. Acta Cryst. A53, 291-313.) The method, like its parent, is unique that it does not rely on ``back'' transformation from the diffraction pattern into real space and on interpolation within measured data. It is designed to deal successfully with sparse, irregular, incomplete and noisy data. It is also designed to use prior information for ensuring sensible results and for reliable convergence. This article describes the theoretical basis for the reconstruction algorithm, its implementation and quantitative results of tests on synthetic and experimentally obtained data. The program could be used for determining the structure of radiation tolerant samples and, eventually, of large biological molecular structures without the need for crystallization.
24 citations
TL;DR: SPEDEN as mentioned in this paper is a computer program that reconstructs the electron density of single particles from their X-ray diffraction patterns, using a single-particle adaptation of the holographic method in crystallography.
Abstract: SPEDEN is a computer program that reconstructs the electron density of single particles from their X-ray diffraction patterns, using a single-particle adaptation of the holographic method in crystallography [Szoke, Szoke & Somoza (1997). Acta Cryst. A53, 291-313]. The method, like its parent, is unique because it does not rely on 'back' transformation from the diffraction pattern into real space and on interpolation within measured data. It is designed to deal successfully with sparse, irregular, incomplete and noisy data. It is also designed to use prior information for ensuring sensible results and for reliable convergence. This article describes the theoretical basis for the reconstruction algorithm, its implementation, and quantitative results of tests on synthetic and experimentally obtained data. The program could be used for determining the structures of radiation-tolerant samples and, eventually, of large biological molecular structures without the need for crystallization.
24 citations
TL;DR: In this article, a new phasing algorithm was used to determine the phases of diffuse elastic X-ray scattering from a nonperiodic array of gold balls of 50 nm diameter.
Abstract: A new phasing algorithm has been used to determine the phases of diffuse elastic X-ray scattering from a non-periodic array of gold balls of 50 nm diameter. Two-dimensional real-space images, showing the charge-density distribution of the balls, have been reconstructed at 50 nm resolution from transmission diffraction patterns recorded at 550 eV energy. The reconstructed image fits well with a scanning-electron-microscope (SEM) image of the same sample. The algorithm, which uses only the density modification portion of the SIR2002 program, is compared with the results obtained via the Gerchberg-Saxton-Fienup HiO algorithm. The new algorithm requires no knowledge of the object's boundary and proceeds from low to high resolution. In this way, the relationship between density modification in crystallography and the HiO algorithm used in signal and image processing is elucidated.
7 citations
TL;DR: A new phasing algorithm has been used to determine the phases of diffuse elastic X-ray scattering from a non-periodic array of gold balls and the relationship between density modification in crystallography and the HiO algorithm used in signal and image processing is elucidated.
Abstract: A new phasing algorithm has been used to determine the phases of diffuse elastic X-ray scattering from a non-periodic array of gold balls of 50 nm diameter. Two-dimensional real-space images, showing the charge-density distribution of the balls, have been reconstructed at 50 nm resolution from transmission diffraction patterns recorded at 550 eV energy. The reconstructed image fits well with scanning electron microscope (SEM) image of the same sample. The algorithm, which uses only the density modification portion of the SIR2002 program, is compared with the results obtained via the Gerchberg-Saxton-Fienup HIO algorithm. In this way the relationship between density modification in crystallography and the HiO algorithm used in signal and image processing is elucidated.
28 Jun 2004
TL;DR: X-ray free-electron lasers will produce pulses of X-rays that are 10 orders of magnitude brighter than today's undulator sources at synchrotrons.
Abstract: X-ray free-electron lasers will produce pulses of X-rays that are 10 orders of magnitude brighter than today's undulator sources at synchrotrons. This may enable atomic resolution imaging of single macromolecules.
01 Jan 2004
TL;DR: X-ray free-electron lasers will produce pulses of X-rays that are 10 orders of magnitude brighter than today's undulator sources at synchrotrons.
Abstract: X-ray free-electron lasers will produce pulses of X-rays that are 10 orders of magnitude brighter than today's undulator sources at synchrotrons. This may enable atomic resolution imaging of single macromolecules.