H. N. Chapman

Bio: H. N. Chapman is an academic researcher. The author has contributed to research in topics: Diffraction & Bragg's law. The author has an hindex of 1, co-authored 1 publications receiving 163 citations.

Macromolecular Imaging using X-ray free-electron lasers*

Abstract: X-ray crystallography, which is used for the determination of most biomolecular structures, has relied on Bragg diffraction from single crystals for more than a century. For many difficult to crystallize proteins, the growth of large well-ordered single crystals is a major challenge. Single molecule diffraction is a challenging but highly desired approach to structure determination, as it abolishes the need for crystallization and provides about four times higher information content than needed to solve a structure, unlike Bragg diffraction which is usually insufficient for direct phasing. Even using the powerful X-ray Free Electron Lasers, the challenges of this method have so far not been overcome to acquire atomic resolution structures. Recently, it was shown that the structure of a protein can be solved based on continuous diffraction from crystals with translational disorder.

The Cambridge Structural Database

Abstract: The Cambridge Structural Database (CSD) contains a complete record of all published organic and metal–organic small-molecule crystal structures. The database has been in operation for over 50 years and continues to be the primary means of sharing structural chemistry data and knowledge across disciplines. As well as structures that are made public to support scientific articles, it includes many structures published directly as CSD Communications. All structures are processed both computationally and by expert structural chemistry editors prior to entering the database. A key component of this processing is the reliable association of the chemical identity of the structure studied with the experimental data. This important step helps ensure that data is widely discoverable and readily reusable. Content is further enriched through selective inclusion of additional experimental data. Entries are available to anyone through free CSD community web services. Linking services developed and maintained by the CCDC, combined with the use of standard identifiers, facilitate discovery from other resources. Data can also be accessed through CCDC and third party software applications and through an application programming interface.

X-ray diffraction from isolated and strongly aligned gas-phase molecules with a free-electron laser

Abstract: We report experimental results on x-ray diffraction of quantum-state-selected and strongly aligned ensembles of the prototypical asymmetric rotor molecule 2,5-diiodobenzonitrile using the Linac Coherent Light Source The experiments demonstrate first steps toward a new approach to diffractive imaging of distinct structures of individual, isolated gas-phase molecules We confirm several key ingredients of single molecule diffraction experiments: the abilities to detect and count individual scattered x-ray photons in single shot diffraction data, to deliver state-selected, eg, structural-isomer-selected, ensembles of molecules to the x-ray interaction volume, and to strongly align the scattering molecules Our approach, using ultrashort x-ray pulses, is suitable to study ultrafast dynamics of isolated molecules

Relaxed averaged alternating reflections for diffraction imaging

Abstract: We report on progress in algorithms for iterative phase retrieval. The theory of convex optimization is used to develop and to gain insight into counterparts for the nonconvex problem of phase retrieval. We propose a relaxation of averaged alternating reflectors and determine the fixed point set of the related operator in the convex case. A numerical study supports our theoretical observations and demonstrates the effectiveness of the algorithm compared to the current state of the art.