Hagemann, Johannes

[["dc.bibliographiccitation.artnumber","041109"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Applied Physics Letters"],["dc.bibliographiccitation.volume","113"],["dc.contributor.author","Hagemann, Johannes"],["dc.contributor.author","Töpperwien, Mareike"],["dc.contributor.author","Salditt, Tim"],["dc.date.accessioned","2020-04-23T14:35:46Z"],["dc.date.available","2020-04-23T14:35:46Z"],["dc.date.issued","2018"],["dc.description.abstract","X-ray phase contrast imaging based on free space propagation relies on phase retrieval to obtain sharp images of micro- and nanoscale objects, with widespread applications in material science and biomedical research. For high resolution synchrotron experiments, phase retrieval is largely based on the single step reconstruction using the contrast transfer function approach (CTF), as introduced almost twenty years ago [Cloetens et al., Appl. Phys. Lett. 75, 2912 (1999)]. Notwithstanding its tremendous merits, this scheme makes stringent assumptions on the optical properties of the object, requiring, in particular, a weakly varying phase. In this work, we show how significant the loss in image quality becomes if these assumption are violated, and how phase retrieval can be easily improved by a simple scheme of alternating projections. Importantly, the approach demonstrated here uses the same input data and constraint sets as the conventional CTF-based phase retrieval, and is particularly well suited for the holographic regime."],["dc.identifier.doi","10.1063/1.5029927"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/64332"],["dc.language.iso","en"],["dc.relation.eissn","1077-3118"],["dc.relation.issn","0003-6951"],["dc.relation.orgunit","Institut für Röntgenphysik"],["dc.relation.workinggroup","RG Salditt (Structure of Biomolecular Assemblies and X-Ray Physics)"],["dc.subject.gro","x-ray imaging"],["dc.title","Phase retrieval for near-field X-ray imaging beyond linearisation or compact support"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","10661"],["dc.bibliographiccitation.issue","12"],["dc.bibliographiccitation.journal","ACS Nano"],["dc.bibliographiccitation.lastpage","10670"],["dc.bibliographiccitation.volume","10"],["dc.contributor.author","Hémonnot, Clément Y. J."],["dc.contributor.author","Ranke, Christiane"],["dc.contributor.author","Saldanha, Oliva"],["dc.contributor.author","Graceffa, Rita"],["dc.contributor.author","Hagemann, Johannes"],["dc.contributor.author","Köster, Sarah"],["dc.date.accessioned","2017-11-28T10:03:27Z"],["dc.date.available","2017-11-28T10:03:27Z"],["dc.date.issued","2016"],["dc.description.abstract","X-ray imaging of intact biological cells is emerging as a complementary method to visible light or electron microscopy. Owing to the high penetration depth and small wavelength of X-rays, it is possible to resolve subcellular structures at a resolution of a few nanometers. Here, we apply scanning X-ray nanodiffraction in combination with time-lapse bright-field microscopy to nuclei of 3T3 fibroblasts and thus relate the observed structures to specific phases in the cell division cycle. We scan the sample at a step size of 250 nm and analyze the individual diffraction patterns according to a generalized Porod’s law. Thus, we obtain information on the aggregation state of the nuclear DNA at a real space resolution on the order of the step size and in parallel structural information on the order of few nanometers. We are able to distinguish nucleoli, heterochromatin, and euchromatin in the nuclei and follow the compaction and decompaction during the cell division cycle."],["dc.identifier.doi","10.1021/acsnano.6b05034"],["dc.identifier.fs","623722"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/10593"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.relation.eissn","1936-086X"],["dc.relation.issn","1936-0851"],["dc.relation.orgunit","Institut für Röntgenphysik"],["dc.relation.workinggroup","RG Köster (Cellular Biophysics)"],["dc.subject","biological cells; cell division cycle; DNA compaction; nanostructure; X-ray nanodiffraction"],["dc.subject.gro","x-ray imaging"],["dc.subject.gro","x-ray scattering"],["dc.subject.gro","cellular biophysics"],["dc.title","Following DNA Compaction During the Cell Cycle by X-ray Nanodiffraction"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","unknown"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","40"],["dc.bibliographiccitation.issue","S2"],["dc.bibliographiccitation.journal","Microscopy and Microanalysis"],["dc.bibliographiccitation.lastpage","41"],["dc.bibliographiccitation.volume","24"],["dc.contributor.author","Hagemann, Johannes"],["dc.contributor.author","Töpperwien, Mareike"],["dc.contributor.author","Salditt, Tim"],["dc.date.accessioned","2020-03-04T13:38:24Z"],["dc.date.available","2020-03-04T13:38:24Z"],["dc.date.issued","2018"],["dc.identifier.doi","10.1017/S143192761801262X"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/63108"],["dc.language.iso","en"],["dc.relation.issn","1431-9276"],["dc.relation.issn","1435-8115"],["dc.relation.orgunit","Institut für Röntgenphysik"],["dc.relation.workinggroup","RG Salditt (Structure of Biomolecular Assemblies and X-Ray Physics)"],["dc.subject.gro","x-ray optics"],["dc.subject.gro","x-ray imaging"],["dc.title","Solving the Phase Problem in X-Ray Near-Field Holography Beyond the Assumption of Weak Objects"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1196"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Journal of Synchrotron Radiation"],["dc.bibliographiccitation.lastpage","1205"],["dc.bibliographiccitation.volume","25"],["dc.contributor.author","Nicolas, Jan-David"],["dc.contributor.author","Hagemann, Johannes"],["dc.contributor.author","Sprung, Michael"],["dc.contributor.author","Salditt, Tim"],["dc.date.accessioned","2020-12-10T18:25:58Z"],["dc.date.available","2020-12-10T18:25:58Z"],["dc.date.issued","2018"],["dc.description.abstract","For almost half a century, optical tweezers have successfully been used to micromanipulate micrometre and sub-micrometre-sized particles. However, in recent years it has been shown experimentally that, compared with single-beam traps, the use of two opposing and divergent laser beams can be more suitable in studying the elastic properties of biological cells and vesicles. Such a configuration is termed an optical stretcher due to its capability of applying high deforming forces on biological objects such as cells. In this article the experimental capabilities of an optical stretcher as a potential sample delivery system for X-ray diffraction and imaging studies at synchrotrons and X-ray free-electron laser (FEL) facilites are demonstrated. To highlight the potential of the optical stretcher its micromanipulation capabilities have been used to image polymer beads and label biological cells. Even in a non-optimized configuration based on a commercially available optical stretcher system, X-ray holograms could be recorded from different views on a biological cell and the three-dimensional phase of the cell could be reconstructed. The capability of the setup to deform cells at higher laser intensities in combination with, for example, X-ray diffraction studies could furthermore lead to interesting studies that couple structural parameters to elastic properties. By means of high-throughput screening, the optical stretcher could become a useful tool in X-ray studies employing synchrotron radiation, and, at a later stage, femtosecond X-ray pulses delivered by X-ray free-electron lasers."],["dc.identifier.doi","10.1107/S1600577518006574"],["dc.identifier.issn","1600-5775"],["dc.identifier.pmid","29979182"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/75896"],["dc.language.iso","en"],["dc.notes.intern","DOI Import GROB-354"],["dc.relation.eissn","1600-5775"],["dc.relation.issn","1600-5775"],["dc.relation.orgunit","Institut für Röntgenphysik"],["dc.relation.workinggroup","RG Salditt (Structure of Biomolecular Assemblies and X-Ray Physics)"],["dc.subject.gro","x-ray imaging"],["dc.subject.gro","x-ray scattering"],["dc.title","The optical stretcher as a tool for single-particle X-ray imaging and diffraction"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","242"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Optics Express"],["dc.bibliographiccitation.lastpage","253"],["dc.bibliographiccitation.volume","26"],["dc.contributor.author","Hagemann, Johannes"],["dc.contributor.author","Salditt, Tim"],["dc.date.accessioned","2022-06-08T07:57:24Z"],["dc.date.available","2022-06-08T07:57:24Z"],["dc.date.issued","2018"],["dc.description.abstract","We 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."],["dc.description.sponsorship"," Bundesministerium für Bildung und Forschung (BMBF) http://dx.doi.org/10.13039/501100002347"],["dc.description.sponsorship"," Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659"],["dc.identifier.doi","10.1364/oe.26.000242"],["dc.identifier.gro","3142482"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/110081"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/13634"],["dc.language.iso","en"],["dc.notes.intern","DOI-Import GROB-575"],["dc.notes.status","final"],["dc.relation.eissn","1094-4087"],["dc.relation.issn","1094-4087"],["dc.relation.orgunit","Institut für Röntgenphysik"],["dc.relation.workinggroup","RG Salditt (Structure of Biomolecular Assemblies and X-Ray Physics)"],["dc.subject.gro","x-ray imaging"],["dc.title","Coherence-resolution relationship in holographic and coherent diffractive imaging"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]