| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Abreu, P., et al.
(författare)
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Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP
- 2001
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 15-28
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Tidskriftsartikel (refereegranskat)abstract
- Muon pair production in the process e+e- → e+e- μ+μ- is studied using the data taken at LEP1 (√s ≃ mz) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb-1. The QED predictions have been tested over the whole Q2 range accessible at LEP1 (from several GeV2/c4 to several hundred GeV2/c4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function Fγ 2. Azimuthal correlations are used to obtain information on additional structure functions, Fγ A and Fγ B, which originate from interference terms of the scattering amplitudes. The measured ratios Fγ A/Fγ 2 and FγB/Fγ 2 are significantly different from zero and consistent with QED predictions.
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| 3. |
- Abreu, P., et al.
(författare)
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Measurement of the gluon fragmentation function and a comparison of the scaling violation in gluon and quark jets
- 2000
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 13:4, s. 573-589
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data set collected with the DELPHI detector at the Z resonance between 1992 and 995. The results at different values of transverse momentum-like scales are compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy e+e- annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio CA/CF is measured to be: CA/CF = 2.26 ± 0.09stat. ± 0.06sys. ± 0.12clus.,scale..
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| 4. |
- Boutet, S., et al.
(författare)
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High-Resolution Protein Structure Determination by Serial Femtosecond Crystallography
- 2012
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 337:6092, s. 362-364
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Tidskriftsartikel (refereegranskat)abstract
- Structure determination of proteins and other macromolecules has historically required the growth of high-quality crystals sufficiently large to diffract x-rays efficiently while withstanding radiation damage. We applied serial femtosecond crystallography (SFX) using an x-ray free-electron laser (XFEL) to obtain high-resolution structural information from microcrystals (less than 1 micrometer by 1 micrometer by 3 micrometers) of the well-characterized model protein lysozyme. The agreement with synchrotron data demonstrates the immediate relevance of SFX for analyzing the structure of the large group of difficult-to-crystallize molecules.
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| 5. |
- Arnlund, David, et al.
(författare)
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Visualizing a protein quake with time-resolved X-ray scattering at a free-electron laser
- 2014
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Ingår i: Nature Methods. - : Springer Science and Business Media LLC. - 1548-7091 .- 1548-7105. ; 11:9, s. 923-926
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Tidskriftsartikel (refereegranskat)abstract
- We describe a method to measure ultrafast protein structural changes using time-resolved wide-angle X-ray scattering at an X-ray free-electron laser. We demonstrated this approach using multiphoton excitation of the Blastochloris viridis photosynthetic reaction center, observing an ultrafast global conformational change that arises within picoseconds and precedes the propagation of heat through the protein. This provides direct structural evidence for a 'protein quake': the hypothesis that proteins rapidly dissipate energy through quake-like structural motions.
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| 6. |
- Barty, A., et al.
(författare)
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Self-terminating diffraction gates femtosecond X-ray nanocrystallography measurements
- 2012
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Ingår i: Nature Photonics. - 1749-4885 .- 1749-4893. ; 6:1, s. 35-40
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers have enabled new approaches to the structural determination of protein crystals that are too small or radiation-sensitive for conventional analysis1. For sufficiently short pulses, diffraction is collected before significant changes occur to the sample, and it has been predicted that pulses as short as 10 fs may be required to acquire atomic-resolution structural information1, 2, 3, 4. Here, we describe a mechanism unique to ultrafast, ultra-intense X-ray experiments that allows structural information to be collected from crystalline samples using high radiation doses without the requirement for the pulse to terminate before the onset of sample damage. Instead, the diffracted X-rays are gated by a rapid loss of crystalline periodicity, producing apparent pulse lengths significantly shorter than the duration of the incident pulse. The shortest apparent pulse lengths occur at the highest resolution, and our measurements indicate that current X-ray free-electron laser technology5 should enable structural determination from submicrometre protein crystals with atomic resolution.
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| 7. |
- Munke, Anna, et al.
(författare)
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Data Descriptor : Coherent diffraction of single Rice Dwarf virus particles using hard X-rays at the Linac Coherent Light Source
- 2016
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Ingår i: Scientific Data. - : Nature Publishing Group. - 2052-4463. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- Single particle diffractive imaging data from Rice Dwarf Virus (RDV) were recorded using the Coherent X-ray Imaging (CXI) instrument at the Linac Coherent Light Source (LCLS). RDV was chosen as it is a wellcharacterized model system, useful for proof-of-principle experiments, system optimization and algorithm development. RDV, an icosahedral virus of about 70 nm in diameter, was aerosolized and injected into the approximately 0.1 mu m diameter focused hard X-ray beam at the CXI instrument of LCLS. Diffraction patterns from RDV with signal to 5.9 angstrom ngstrom were recorded. The diffraction data are available through the Coherent X-ray Imaging Data Bank (CXIDB) as a resource for algorithm development, the contents of which are described here.
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| 8. |
- Chapman, Henry N, et al.
(författare)
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Femtosecond X-ray protein nanocrystallography.
- 2011
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 470:7332, s. 73-7
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Tidskriftsartikel (refereegranskat)abstract
- X-ray crystallography provides the vast majority of macromolecular structures, but the success of the method relies on growing crystals of sufficient size. In conventional measurements, the necessary increase in X-ray dose to record data from crystals that are too small leads to extensive damage before a diffraction signal can be recorded. It is particularly challenging to obtain large, well-diffracting crystals of membrane proteins, for which fewer than 300 unique structures have been determined despite their importance in all living cells. Here we present a method for structure determination where single-crystal X-ray diffraction 'snapshots' are collected from a fully hydrated stream of nanocrystals using femtosecond pulses from a hard-X-ray free-electron laser, the Linac Coherent Light Source. We prove this concept with nanocrystals of photosystem I, one of the largest membrane protein complexes. More than 3,000,000 diffraction patterns were collected in this study, and a three-dimensional data set was assembled from individual photosystem I nanocrystals (∼200nm to 2μm in size). We mitigate the problem of radiation damage in crystallography by using pulses briefer than the timescale of most damage processes. This offers a new approach to structure determination of macromolecules that do not yield crystals of sufficient size for studies using conventional radiation sources or are particularly sensitive to radiation damage.
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| 9. |
- Hantke, Max F., et al.
(författare)
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High-throughput imaging of heterogeneous cell organelles with an X-ray laser
- 2014
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 8:12, s. 943-949
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Tidskriftsartikel (refereegranskat)abstract
- We overcome two of the most daunting challenges in single-particle diffractive imaging: collecting many high-quality diffraction patterns on a small amount of sample and separating components from mixed samples. We demonstrate this on carboxysomes, which are polyhedral cell organelles that vary in size and facilitate up to 40% of Earth's carbon fixation. A new aerosol sample-injector allowed us to record 70,000 low-noise diffraction patterns in 12 min with the Linac Coherent Light Source running at 120 Hz. We separate different structures directly from the diffraction data and show that the size distribution is preserved during sample delivery. We automate phase retrieval and avoid reconstruction artefacts caused by missing modes. We attain the highest-resolution reconstructions on the smallest single biological objects imaged with an X-ray laser to date. These advances lay the foundations for accurate, high-throughput structure determination by flash-diffractive imaging and offer a means to study structure and structural heterogeneity in biology and elsewhere.
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| 10. |
- Loh, N. D., et al.
(författare)
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Cryptotomography : Reconstructing 3D Fourier Intensities from Randomly Oriented Single-Shot Diffraction Patterns
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:22, s. 225501-1-225501-5
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Tidskriftsartikel (refereegranskat)abstract
- We reconstructed the 3D Fourier intensity distribution of monodisperse prolate nanoparticles using single-shot 2D coherent diffraction patterns collected at DESY's FLASH facility when a bright, coherent, ultrafast x-ray pulse intercepted individual particles of random, unmeasured orientations. This first experimental demonstration of cryptotomography extended the expansion-maximization-compression framework to accommodate unmeasured fluctuations in photon fluence and loss of data due to saturation or background scatter. This work is an important step towards realizing single-shot diffraction imaging of single biomolecules.
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| 11. |
- Lundholm, Ida V., et al.
(författare)
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Considerations for three-dimensional image reconstruction from experimental data in coherent diffractive imaging
- 2018
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Ingår i: IUCrJ. - : International Union of Crystallography. - 2052-2525. ; 5, s. 531-541
-
Tidskriftsartikel (refereegranskat)abstract
- Diffraction before destruction using X-ray free-electron lasers (XFELs) has the potential to determine radiation-damage-free structures without the need for crystallization. This article presents the three-dimensional reconstruction of the Melbournevirus from single-particle X-ray diffraction patterns collected at the LINAC Coherent Light Source (LCLS) as well as reconstructions from simulated data exploring the consequences of different kinds of experimental sources of noise. The reconstruction from experimental data suffers from a strong artifact in the center of the particle. This could be reproduced with simulated data by adding experimental background to the diffraction patterns. In those simulations, the relative density of the artifact increases linearly with background strength. This suggests that the artifact originates from the Fourier transform of the relatively flat background, concentrating all power in a central feature of limited extent. We support these findings by significantly reducing the artifact through background removal before the phase-retrieval step. Large amounts of blurring in the diffraction patterns were also found to introduce diffuse artifacts, which could easily be mistaken as biologically relevant features. Other sources of noise such as sample heterogeneity and variation of pulse energy did not significantly degrade the quality of the reconstructions. Larger data volumes, made possible by the recent inauguration of high repetition-rate XFELs, allow for increased signal-to-background ratio and provide a way to minimize these artifacts. The anticipated development of three-dimensional Fourier-volume-assembly algorithms which are background aware is an alternative and complementary solution, which maximizes the use of data.
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| 12. |
- Reddy, Hemanth K. N., et al.
(författare)
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Coherent soft X-ray diffraction imaging of coliphage PR772 at the Linac coherent light source
- 2017
-
Ingår i: Scientia Danica. Series H. Humanistica 4. - : Nature Publishing Group. - 1904-5506 .- 2052-4463. ; 4
-
Tidskriftsartikel (refereegranskat)abstract
- Single-particle diffraction from X-ray Free Electron Lasers offers the potential for molecular structure determination without the need for crystallization. In an effort to further develop the technique, we present a dataset of coherent soft X-ray diffraction images of Coliphage PR772 virus, collected at the Atomic Molecular Optics (AMO) beamline with pnCCD detectors in the LAMP instrument at the Linac Coherent Light Source. The diameter of PR772 ranges from 65-70 nm, which is considerably smaller than the previously reported similar to 600 nm diameter Mimivirus. This reflects continued progress in XFEL-based single-particle imaging towards the single molecular imaging regime. The data set contains significantly more single particle hits than collected in previous experiments, enabling the development of improved statistical analysis, reconstruction algorithms, and quantitative metrics to determine resolution and self-consistency.
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| 13. |
- van der Schot, Gijs, et al.
(författare)
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Open data set of live cyanobacterial cells imaged using an X-ray laser
- 2016
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- Structural studies on living cells by conventional methods are limited to low resolution because radiation damage kills cells long before the necessary dose for high resolution can be delivered. X-ray free-electron lasers circumvent this problem by outrunning key damage processes with an ultra-short and extremely bright coherent X-ray pulse. Diffraction-before-destruction experiments provide high-resolution data from cells that are alive when the femtosecond X-ray pulse traverses the sample. This paper presents two data sets from micron-sized cyanobacteria obtained at the Linac Coherent Light Source, containing a total of 199,000 diffraction patterns. Utilizing this type of diffraction data will require the development of new analysis methods and algorithms for studying structure and structural variability in large populations of cells and to create abstract models. Such studies will allow us to understand living cells and populations of cells in new ways. New X-ray lasers, like the European XFEL, will produce billions of pulses per day, and could open new areas in structural sciences.
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| 14. |
- Aquila, Andrew, et al.
(författare)
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Time-resolved protein nanocrystallography using an X-ray free-electron laser
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:3, s. 2706-2716
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the use of an X-ray free electron laser synchronized with an optical pump laser to obtain X-ray diffraction snapshots from the photoactivated states of large membrane protein complexes in the form of nanocrystals flowing in a liquid jet. Light-induced changes of Photosystem I-Ferredoxin co-crystals were observed at time delays of 5 to 10 µs after excitation. The result correlates with the microsecond kinetics of electron transfer from Photosystem I to ferredoxin. The undocking process that follows the electron transfer leads to large rearrangements in the crystals that will terminally lead to the disintegration of the crystals. We describe the experimental setup and obtain the first time-resolved femtosecond serial X-ray crystallography results from an irreversible photo-chemical reaction at the Linac Coherent Light Source. This technique opens the door to time-resolved structural studies of reaction dynamics in biological systems.
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| 15. |
- Bielecki, Johan, 1982, et al.
(författare)
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Electrospray sample injection for single-particle imaging with x-ray lasers
- 2019
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Ingår i: Science advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:5
-
Tidskriftsartikel (refereegranskat)abstract
- The possibility of imaging single proteins constitutes an exciting challenge for x-ray lasers. Despite encouraging results on large particles, imaging small particles has proven to be difficult for two reasons: not quite high enough pulse intensity from currently available x-ray lasers and, as we demonstrate here, contamination of the aerosolized molecules by nonvolatile contaminants in the solution. The amount of contamination on the sample depends on the initial droplet size during aerosolization. Here, we show that, with our electrospray injector, we can decrease the size of aerosol droplets and demonstrate virtually contaminant-free sample delivery of organelles, small virions, and proteins. The results presented here, together with the increased performance of next-generation x-ray lasers, constitute an important stepping stone toward the ultimate goal of protein structure determination from imaging at room temperature and high temporal resolution.
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| 16. |
- Brändén, Gisela, 1975, et al.
(författare)
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Coherent diffractive imaging of microtubules using an X-ray laser.
- 2019
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Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray free electron lasers (XFELs) create new possibilities for structural studies of biological objects that extend beyond what is possible with synchrotron radiation. Serial femtosecond crystallography has allowed high-resolution structures to be determined from micro-meter sized crystals, whereas single particle coherent X-ray imaging requires development to extend the resolution beyond a few tens of nanometers. Here we describe an intermediate approach: the XFEL imaging of biological assemblies with helical symmetry. We collected X-ray scattering images from samples of microtubules injected across an XFEL beam using a liquid microjet, sorted these images into class averages, merged these data into a diffraction pattern extending to 2nm resolution, and reconstructed these data into a projection image of the microtubule. Details such as the 4nm tubulin monomer became visible in this reconstruction. These results illustrate the potential of single-molecule X-ray imaging of biological assembles with helical symmetry at room temperature.
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| 17. |
- Daurer, Benedikt J., et al.
(författare)
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Experimental strategies for imaging bioparticles with femtosecond hard X-ray pulses
- 2017
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Ingår i: IUCrJ. - : INT UNION CRYSTALLOGRAPHY. - 2052-2525. ; 4, s. 251-262
-
Tidskriftsartikel (refereegranskat)abstract
- This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of similar to 40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from similar to 35 to similar to 300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 * 10(12) photons per mu m(2) per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.
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| 18. |
- Ekeberg, Tomas, et al.
(författare)
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Single-shot diffraction data from the Mimivirus particle using an X-ray free-electron laser
- 2016
-
Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- Free-electron lasers (FEL) hold the potential to revolutionize structural biology by producing X-ray pules short enough to outrun radiation damage, thus allowing imaging of biological samples without the limitation from radiation damage. Thus, a major part of the scientific case for the first FELs was three-dimensional (3D) reconstruction of non-crystalline biological objects. In a recent publication we demonstrated the first 3D reconstruction of a biological object from an X-ray FEL using this technique. The sample was the giant Mimivirus, which is one of the largest known viruses with a diameter of 450 nm. Here we present the dataset used for this successful reconstruction. Data-analysis methods for single-particle imaging at FELs are undergoing heavy development but data collection relies on very limited time available through a highly competitive proposal process. This dataset provides experimental data to the entire community and could boost algorithm development and provide a benchmark dataset for new algorithms.
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| 19. |
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| 20. |
- Gorkhover, Tais, et al.
(författare)
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Femtosecond X-ray Fourier holography imaging of free-flying nanoparticles
- 2018
-
Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 12:3, s. 150-153
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrafast X-ray imaging on individual fragile specimens such as aerosols 1 , metastable particles 2 , superfluid quantum systems 3 and live biospecimens 4 provides high-resolution information that is inaccessible with conventional imaging techniques. Coherent X-ray diffractive imaging, however, suffers from intrinsic loss of phase, and therefore structure recovery is often complicated and not always uniquely defined 4,5 . Here, we introduce the method of in-flight holography, where we use nanoclusters as reference X-ray scatterers to encode relative phase information into diffraction patterns of a virus. The resulting hologram contains an unambiguous three-dimensional map of a virus and two nanoclusters with the highest lateral resolution so far achieved via single shot X-ray holography. Our approach unlocks the benefits of holography for ultrafast X-ray imaging of nanoscale, non-periodic systems and paves the way to direct observation of complex electron dynamics down to the attosecond timescale.
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| 21. |
- Hantke, Max F., et al.
(författare)
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A data set from flash X-ray imaging of carboxysomes
- 2016
-
Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- Ultra-intense femtosecond X-ray pulses from X-ray lasers permit structural studies on single particles and biomolecules without crystals. We present a large data set on inherently heterogeneous, polyhedral carboxysome particles. Carboxysomes are cell organelles that vary in size and facilitate up to 40% of Earth’s carbon fixation by cyanobacteria and certain proteobacteria. Variation in size hinders crystallization. Carboxysomes appear icosahedral in the electron microscope. A protein shell encapsulates a large number of Rubisco molecules in paracrystalline arrays inside the organelle. We used carboxysomes with a mean diameter of 115±26 nm from Halothiobacillus neapolitanus. A new aerosol sample-injector allowed us to record 70,000 low-noise diffraction patterns in 12 min. Every diffraction pattern is a unique structure measurement and high-throughput imaging allows sampling the space of structural variability. The different structures can be separated and phased directly from the diffraction data and open a way for accurate, high-throughput studies on structures and structural heterogeneity in biology and elsewhere.
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| 22. |
- Huynh-Le, MP, et al.
(författare)
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Polygenic hazard score is associated with prostate cancer in multi-ethnic populations
- 2021
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Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1, s. 1236-
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Tidskriftsartikel (refereegranskat)abstract
- Genetic models for cancer have been evaluated using almost exclusively European data, which could exacerbate health disparities. A polygenic hazard score (PHS1) is associated with age at prostate cancer diagnosis and improves screening accuracy in Europeans. Here, we evaluate performance of PHS2 (PHS1, adapted for OncoArray) in a multi-ethnic dataset of 80,491 men (49,916 cases, 30,575 controls). PHS2 is associated with age at diagnosis of any and aggressive (Gleason score ≥ 7, stage T3-T4, PSA ≥ 10 ng/mL, or nodal/distant metastasis) cancer and prostate-cancer-specific death. Associations with cancer are significant within European (n = 71,856), Asian (n = 2,382), and African (n = 6,253) genetic ancestries (p < 10−180). Comparing the 80th/20th PHS2 percentiles, hazard ratios for prostate cancer, aggressive cancer, and prostate-cancer-specific death are 5.32, 5.88, and 5.68, respectively. Within European, Asian, and African ancestries, hazard ratios for prostate cancer are: 5.54, 4.49, and 2.54, respectively. PHS2 risk-stratifies men for any, aggressive, and fatal prostate cancer in a multi-ethnic dataset.
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| 23. |
- Johansson, Linda C, 1983, et al.
(författare)
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Lipidic phase membrane protein serial femtosecond crystallography.
- 2012
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Ingår i: Nature methods. - : Springer Science and Business Media LLC. - 1548-7105 .- 1548-7091. ; 9:3, s. 263-265
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free electron laser (X-FEL)-based serial femtosecond crystallography is an emerging method with potential to rapidly advance the challenging field of membrane protein structural biology. Here we recorded interpretable diffraction data from micrometer-sized lipidic sponge phase crystals of the Blastochloris viridis photosynthetic reaction center delivered into an X-FEL beam using a sponge phase micro-jet.
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| 24. |
- Johansson, Linda C, 1983, et al.
(författare)
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Structure of a photosynthetic reaction centre determined by serial femtosecond crystallography.
- 2013
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Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4
-
Tidskriftsartikel (refereegranskat)abstract
- Serial femtosecond crystallography is an X-ray free-electron-laser-based method with considerable potential to have an impact on challenging problems in structural biology. Here we present X-ray diffraction data recorded from microcrystals of the Blastochloris viridis photosynthetic reaction centre to 2.8Å resolution and determine its serial femtosecond crystallography structure to 3.5Å resolution. Although every microcrystal is exposed to a dose of 33MGy, no signs of X-ray-induced radiation damage are visible in this integral membrane protein structure.
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| 25. |
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| 26. |
- Koopmann, Rudolf, et al.
(författare)
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In vivo protein crystallization opens new routes in structural biology
- 2012
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Ingår i: Nature Methods. - : Springer Science and Business Media LLC. - 1548-7091 .- 1548-7105. ; 9:3, s. 259-262
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Tidskriftsartikel (refereegranskat)abstract
- Protein crystallization in cells has been observed several times in nature. However, owing to their small size these crystals have not yet been used for X-ray crystallographic analysis. We prepared nano-sized in vivo–grown crystals of Trypanosoma brucei enzymes and applied the emerging method of free-electron laser-based serial femtosecond crystallography to record interpretable diffraction data. This combined approach will open new opportunities in structural systems biology.
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| 27. |
- Kupitz, Christopher, et al.
(författare)
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Serial time-resolved crystallography of photosystem II using a femtosecond X-ray laser
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 513:7517, s. 261-265
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthesis, a process catalysed by plants, algae and cyanobacteria converts sunlight to energy thus sustaining all higher life on Earth. Two large membrane protein complexes, photosystem I and II (PSI and PSII), act in series to catalyse the light-driven reactions in photosynthesis. PSII catalyses the light-driven water splitting process, which maintains the Earth's oxygenic atmosphere. In this process, the oxygen-evolving complex (OEC) of PSII cycles through five states, S0 to S4, in which four electrons are sequentially extracted from the OEC in four light-driven charge-separation events. Here we describe time resolved experiments on PSII nano/microcrystals from Thermosynechococcus elongatus performed with the recently developed technique of serial femtosecond crystallography. Structures have been determined from PSII in the dark S1 state and after double laser excitation (putative S3 state) at 5 and 5.5 Å resolution, respectively. The results provide evidence that PSII undergoes significant conformational changes at the electron acceptor side and at the Mn4CaO5 core of the OEC. These include an elongation of the metal cluster, accompanied by changes in the protein environment, which could allow for binding of the second substrate water molecule between the more distant protruding Mn (referred to as the 'dangler' Mn) and the Mn3CaOx cubane in the S2 to S3 transition, as predicted by spectroscopic and computational studies. This work shows the great potential for time-resolved serial femtosecond crystallography for investigation of catalytic processes in biomolecules.
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| 28. |
- Liu, Wei, et al.
(författare)
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Serial Femtosecond Crystallography of G Protein-Coupled Receptors
- 2013
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 342:6165, s. 1521-1524
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Tidskriftsartikel (refereegranskat)abstract
- X-ray crystallography of G protein-coupled receptors and other membrane proteins is hampered by difficulties associated with growing sufficiently large crystals that withstand radiation damage and yield high-resolution data at synchrotron sources. We used an x-ray free-electron laser (XFEL) with individual 50-femtosecond-duration x-ray pulses to minimize radiation damage and obtained a high-resolution room-temperature structure of a human serotonin receptor using sub-10-micrometer microcrystals grown in a membrane mimetic matrix known as lipidic cubic phase. Compared with the structure solved by using traditional microcrystallography from cryo-cooled crystals of about two orders of magnitude larger volume, the room-temperature XFEL structure displays a distinct distribution of thermal motions and conformations of residues that likely more accurately represent the receptor structure and dynamics in a cellular environment.
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| 29. |
- Lomb, Lukas, et al.
(författare)
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Radiation damage in protein serial femtosecond crystallography using an x-ray free-electron laser
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:21, s. 214111-1-214111-6
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers deliver intense femtosecond pulses that promise to yield high resolution diffraction data of nanocrystals before the destruction of the sample by radiation damage. Diffraction intensities of lysozyme nanocrystals collected at the Linac Coherent Light Source using 2 keV photons were used for structure determination by molecular replacement and analyzed for radiation damage as a function of pulse length and fluence. Signatures of radiation damage are observed for pulses as short as 70 fs. Parametric scaling used in conventional crystallography does not account for the observed effects.
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| 30. |
- Rath, Asawari D., et al.
(författare)
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Explosion dynamics of sucrose nanospheres monitored by time of flight spectrometry and coherent diffractive imaging at the split-and-delay beam line of the FLASH soft X-ray laser
- 2014
-
Ingår i: Optics Express. - 1094-4087. ; 22:23, s. 28914-28925
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Tidskriftsartikel (refereegranskat)abstract
- We use a Mach-Zehnder type autocorrelator to split and delay XUV pulses from the FLASH soft X-ray laser for triggering and subsequently probing the explosion of aerosolised sugar balls. FLASH was running at 182 eV photon energy with pulses of 70 fs duration. The delay between the pump-probe pulses was varied between zero and 5 ps, and the pulses were focused to reach peak intensities above 1016 W/cm2 with an off-axis parabola. The direct pulse triggered the explosion of single aerosolised sucrose nano-particles, while the delayed pulse probed the exploding structure. The ejected ions were measured by ion time of flight spectrometry, and the particle sizes were measured by coherent diffractive imaging. The results show that sucrose particles of 560-1000 nm diameter retain their size for about 500 fs following the first exposure. Significant sample expansion happens between 500 fs and 1 ps. We present simulations to support these observations.
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| 31. |
- Seibert, M. Marvin, et al.
(författare)
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Femtosecond diffractive imaging of biological cells
- 2010
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:19, s. 194015-
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Tidskriftsartikel (refereegranskat)abstract
- In a flash diffraction experiment, a short and extremely intense x-ray pulse illuminates the sample to obtain a diffraction pattern before the onset of significant radiation damage. The over-sampled diffraction pattern permits phase retrieval by iterative phasing methods. Flash diffractive imaging was first demonstrated on an inorganic test object (Chapman et al 2006 Nat. Phys. 2 839-43). We report here experiments on biological systems where individual cells were imaged, using single, 10-15 fs soft x-ray pulses at 13.5 nm wavelength from the FLASH free-electron laser in Hamburg. Simulations show that the pulse heated the sample to about 160 000 K but not before an interpretable diffraction pattern could be obtained. The reconstructed projection images return the structures of the intact cells. The simulations suggest that the average displacement of ions and atoms in the hottest surface layers remained below 3 angstrom during the pulse.
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| 32. |
- Seibert, M. Marvin, et al.
(författare)
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Single mimivirus particles intercepted and imaged with an X-ray laser
- 2011
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 470:7332, s. 78-81
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Tidskriftsartikel (refereegranskat)abstract
- X-ray lasers offer new capabilities in understanding the structure of biological systems, complex materials and matter under extreme conditions(1-4). Very short and extremely bright, coherent X-ray pulses can be used to outrun key damage processes and obtain a single diffraction pattern from a large macromolecule, a virus or a cell before the sample explodes and turns into plasma(1). The continuous diffraction pattern of non-crystalline objects permits oversampling and direct phase retrieval(2). Here we show that high-quality diffraction data can be obtained with a single X-ray pulse from a noncrystalline biological sample, a single mimivirus particle, which was injected into the pulsed beam of a hard-X-ray free-electron laser, the Linac Coherent Light Source(5). Calculations indicate that the energy deposited into the virus by the pulse heated the particle to over 100,000 K after the pulse had left the sample. The reconstructed exit wavefront (image) yielded 32-nm full-period resolution in a single exposure and showed no measurable damage. The reconstruction indicates inhomogeneous arrangement of dense material inside the virion. We expect that significantly higher resolutions will be achieved in such experiments with shorter and brighter photon pulses focused to a smaller area. The resolution in such experiments can be further extended for samples available in multiple identical copies.
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| 33. |
- Sierra, Raymond G., et al.
(författare)
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Nanoflow electrospinning serial femtosecond crystallography
- 2012
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Ingår i: Acta Crystallographica Section D. - : Wiley-Blackwell. - 0907-4449 .- 1399-0047. ; 68, s. 1584-1587
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Tidskriftsartikel (refereegranskat)abstract
- An electrospun liquid microjet has been developed that delivers protein microcrystal suspensions at flow rates of 0.14-3.1 mu l min(-1) to perform serial femtosecond crystallography (SFX) studies with X-ray lasers. Thermolysin microcrystals flowed at 0.17 mu l min(-1) and diffracted to beyond 4 angstrom resolution, producing 14 000 indexable diffraction patterns, or four per second, from 140 mu g of protein. Nanoflow electrospinning extends SFX to biological samples that necessitate minimal sample consumption.
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| 34. |
- Thomas, H., et al.
(författare)
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Explosions of Xenon Clusters in Ultraintense Femtosecond X-Ray Pulses from the LCLS Free Electron Laser
- 2012
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:13
-
Tidskriftsartikel (refereegranskat)abstract
- Explosions of large Xe clusters (< N > similar to 11 000) irradiated by femtosecond pulses of 850 eV x-ray photons focused to an intensity of up to 1017 W/cm(2) from the Linac Coherent Light Source were investigated experimentally. Measurements of ion charge-state distributions and energy spectra exhibit strong evidence for the formation of a Xe nanoplasma in the intense x-ray pulse. This x-ray produced Xe nanoplasma is accompanied by a three-body recombination and hydrodynamic expansion. These experimental results appear to be consistent with a model in which a spherically exploding nanoplasma is formed inside the Xe cluster and where the plasma temperature is determined by photoionization heating.
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| 35. |
- van der Schot, Gijs, et al.
(författare)
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Imaging single cells in a beam of live cyanobacteria with an X-ray laser
- 2015
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- There exists a conspicuous gap of knowledge about the organization of life at mesoscopic levels. Ultra-fast coherent diffractive imaging with X-ray free-electron lasers can probe structures at the relevant length scales and may reach sub-nanometer resolution on micron-sized living cells. Here we show that we can introduce a beam of aerosolised cyanobacteria into the focus of the Linac Coherent Light Source and record diffraction patterns from individual living cells at very low noise levels and at high hit ratios. We obtain two-dimensional projection images directly from the diffraction patterns, and present the results as synthetic X-ray Nomarski images calculated from the complex-valued reconstructions. We further demonstrate that it is possible to record diffraction data to nanometer resolution on live cells with X-ray lasers. Extension to sub-nanometer resolution is within reach, although improvements in pulse parameters and X-ray area detectors will be necessary to unlock this potential.
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| 36. |
- Yoon, Chun Hong, et al.
(författare)
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Unsupervised classification of single-particle X-ray diffraction snapshots by spectral clustering
- 2011
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Ingår i: Optics Express. - 1094-4087. ; 19:17, s. 16542-16549
-
Tidskriftsartikel (refereegranskat)abstract
- Single-particle experiments using X-ray Free Electron Lasers produce more than 10(5) snapshots per hour, consisting of an admixture of blank shots (no particle intercepted), and exposures of one or more particles. Experimental data sets also often contain unintentional contamination with different species. We present an unsupervised method able to sort experimental snapshots without recourse to templates, specific noise models, or user-directed learning. The results show 90% agreement with manual classification.
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| 37. |
- Andreasson, Jakob, et al.
(författare)
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Saturated ablation in metal hydrides and acceleration of protons and deuterons to keV energies with a soft-x-ray laser
- 2011
-
Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 83:1, s. 016403-
-
Tidskriftsartikel (refereegranskat)abstract
- Studies of materials under extreme conditions have relevance to a broad area of research, including planetary physics, fusion research, materials science, and structural biology with x-ray lasers. We study such extreme conditions and experimentally probe the interaction between ultrashort soft x-ray pulses and solid targets (metals and their deuterides) at the FLASH free-electron laser where power densities exceeding 1017 W/cm2 were reached. Time-of-flight ion spectrometry and crater analysis were used to characterize the interaction. The results show the onset of saturation in the ablation process at power densities above 1016 W/cm2. This effect can be linked to a transiently induced x-ray transparency in the solid by the femtosecond x-ray pulse at high power densities. The measured kinetic energies of protons and deuterons ejected from the surface reach several keV and concur with predictions from plasma-expansion models. Simulations of the interactions were performed with a nonlocal thermodynamic equilibrium code with radiation transfer. These calculations return critical depths similar to the observed crater depths and capture the transient surface transparency at higher power densities.
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| 38. |
- Barty, Anton, et al.
(författare)
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Ultrafast single-shot diffraction imaging of nanoscale dynamics
- 2008
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Ingår i: Nature Photonics. - : Springer Science and Business Media LLC. - 1749-4885 .- 1749-4893. ; 2:7, s. 415-419
-
Tidskriftsartikel (refereegranskat)abstract
- The transient nanoscale dynamics of materials on femtosecond to picosecond timescales is of great interest in the study of condensed phase dynamics such as crack formation, phase separation and nucleation, and rapid fluctuations in the liquid state or in biologically relevant environments. The ability to take images in a single shot is the key to studying non-repetitive behaviour mechanisms, a capability that is of great importance in many of these problems. Using coherent diffraction imaging with femtosecond X-ray free-electron-laser pulses we capture time-series snapshots of a solid as it evolves on the ultrafast timescale. Artificial structures imprinted on a Si3N4 window are excited with an optical laser and undergo laser ablation, which is imaged with a spatial resolution of 50 nm and a temporal resolution of 10 ps. By using the shortest available free-electron-laser wavelengths(1) and proven synchronization methods(2) this technique could be extended to spatial resolutions of a few nanometres and temporal resolutions of a few tens of femtoseconds. This experiment opens the door to a new regime of time-resolved experiments in mesoscopic dynamics.
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| 39. |
- Bogan, Michael J., et al.
(författare)
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Aerosol Imaging with a Soft X-Ray Free Electron Laser
- 2010
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Ingår i: Aerosol Science and Technology. - : Informa UK Limited. - 0278-6826 .- 1521-7388. ; 44:3, s. I-VI
-
Tidskriftsartikel (refereegranskat)abstract
- Lasers have long played a critical role in the advancement of aerosol science. A new regime of ultrafast laser technology has recently be realized, the world's first soft x-ray free electron laser. The Free electron LASer in Hamburg, FLASH, user facility produces a steady source of 10 femtosecond pulses of 7–32 nm x-rays with 1012 photons per pulse. The high brightness, short wavelength, and high repetition rate (> 500 pulses per second) of this laser offers unique capabilities for aerosol characterization. Here we use FLASH to perform the highest resolution imaging of single PM2.5 aerosol particles in flight to date. We resolve to 35 nm the morphology of fibrous and aggregated spherical carbonaceous nanoparticles that existed for less than two milliseconds in vacuum. Our result opens the possibility for high spatial- and time-resolved single particle aerosol dynamics studies, filling a critical technological need in aerosol science.
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| 40. |
- Bogan, Michael J, et al.
(författare)
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Single particle X-ray diffractive imaging
- 2008
-
Ingår i: Nano letters (Print). - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 8:1, s. 310-6
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Tidskriftsartikel (refereegranskat)abstract
- In nanotechnology, strategies for the creation and manipulation of nanoparticles in the gas phase are critically important for surface modification and substrate-free characterization. Recent coherent diffractive imaging with intense femtosecond X-ray pulses has verified the capability of single-shot imaging of nanoscale objects at suboptical resolutions beyond the radiation-induced damage threshold. By intercepting electrospray-generated particles with a single 15 femtosecond soft-X-ray pulse, we demonstrate diffractive imaging of a nanoscale specimen in free flight for the first time, an important step toward imaging uncrystallized biomolecules.
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| 41. |
- Bogan, M. J., et al.
(författare)
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Single-shot femtosecond x-ray diffraction from randomly oriented ellipsoidal nanoparticles
- 2010
-
Ingår i: Physical Review Special Topics - Accelerators and Beams. - 1098-4402. ; 13:9, s. 094701-
-
Tidskriftsartikel (refereegranskat)abstract
- Coherent diffractive imaging of single particles using the single-shot "diffract and destroy" approach with an x-ray free electron laser (FEL) was recently demonstrated. A high-resolution low-noise coherent diffraction pattern, representative of the object before it turns into a plasma and explodes, results from the interaction of the FEL with the particle. Iterative phase retrieval algorithms are used to reconstruct two-dimensional projection images of the object from the recorded intensities alone. Here we describe the first single-shot diffraction data set that mimics the data proposed for obtaining 3D structure from identical particles. Ellipsoidal iron oxide nanoparticles (250 nm x 50 nm) were aerosolized and injected through an aerodynamic lens stack into a soft x-ray FEL. Particle orientation was not controlled with this injection method. We observed that, at the instant the x-ray pulse interacts with the particle, a snapshot of the particle's orientation is encoded in the diffraction pattern. The results give credence to one of the technical concepts of imaging individual nanometer and subnanometer-sized objects such as single molecules or larger clusters of molecules using hard x-ray FELs and will be used to help develop robust algorithms for determining particle orientations and 3D structure.
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| 42. |
- Boutet, Sebastien, et al.
(författare)
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Ultrafast soft X-ray scattering and reference-enhanced diffractive imaging of weakly scattering nanoparticles
- 2008
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 166, s. 65-73
-
Tidskriftsartikel (refereegranskat)abstract
- We report the first successful reconstruction of the real space image from coherent X-ray diffraction patterns of membrane-supported nanoparticles using single ultrafast pulses. The particles consisted of 145-nm spherical polystyrene spheres that were size-selected by differential mobility analysis. We investigated the dependence of signal intensity on the number of spherical nanoparticles irradiated by single ultrafast pulses at the FLASH FEL facility. We demonstrate detection of as few as two 145-nm diameter particles irradiated by a single 32 nm fs-long FLASH pulse focused to 2.4Jcm(-2). In this case the noise in the diffraction pattern. due to photon-counting statistics and scattering from the supporting silicon nitride membrane, was the largest contributor to the recorded intensity. We were able to reconstruct high-resolution images of the nanoparticles using a strong scattering reference object to aid the phase retrieval of the coherent diffraction pattern. This method of reference-enhanced diffractive imaging may allow the imaging of weakly scattering objects at FLASH and other future X-ray FEL sources.
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| 43. |
- Breuer, L., et al.
(författare)
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Assessing the impact of land use change on hydrology by ensemble modeling (LUCHEM). I : Model intercomparison with current land use
- 2009
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Ingår i: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 32:2, s. 129-146
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces the project on 'Assessing the impact of land use change on hydrology by ensemble modeling (LUCHEM)' that aims at investigating the envelope of predictions on changes in hydrological fluxes due to land use change. As part of a series of four papers, this paper outlines the motivation and setup of LUCHEM, and presents a model intercomparison for the present-day simulation results. Such an intercomparison provides a valuable basis to investigate the effects of different model structures on model predictions and paves the ground for the analysis of the performance of multi-model ensembles and the reliability of the scenario predictions in companion papers. in this study, we applied a set of 10 lumped, semi-lumped and fully distributed hydrological models that have been previously used in land use change studies to the low mountainous Dill catchment. Germany. Substantial differences in model performance were observed with Nash-Sutcliffe efficiencies ranging from 0.53 to 0.92. Differences in model performance were attributed to (1) model input data, (2) model calibration and (3) the physical basis of the models. The models were applied with two sets of input data: an original and a homogenized data set. This homogenization of precipitation, temperature and leaf area index was performed to reduce the variation between the models. Homogenization improved the comparability of model simulations and resulted in a reduced average bias, although some variation in model data input remained. The effect of the physical differences between models on the long-term water balance was mainly attributed to differences in how models represent evapotranspiration. Semi-lumped and lumped conceptual models slightly outperformed the fully distributed and physically based models. This was attributed to the automatic model calibration typically used for this type of models. Overall, however, we conclude that there was no superior model if several measures of model performance are considered and that all models are suitable to participate in further multi-model ensemble set-ups and land use change scenario investigations.
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| 44. |
- Chapman, H N, et al.
(författare)
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Coherent imaging at FLASH
- 2009
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 186:1, s. 012051-
-
Tidskriftsartikel (refereegranskat)abstract
- We have carried out high-resolution single-pulse coherent diffractive imaging at the FLASH free-electron laser. The intense focused FEL pulse gives a high-resolution low-noise coherent diffraction pattern of an object before that object turns into a plasma and explodes. In particular we are developing imaging of biological specimens beyond conventional radiation damage resolution limits, developing imaging of ultrafast processes, and testing methods to characterize and perform single-particle imaging.
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| 45. |
- Chapman, Henry N., et al.
(författare)
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Femtosecond diffractive imaging with a soft-X-ray free-electron laser
- 2006
-
Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 2:12, s. 839-843
-
Tidskriftsartikel (refereegranskat)abstract
- Theory predicts(1-4) that, with an ultrashort and extremely bright coherent X-ray pulse, a single diffraction pattern may be recorded from a large macromolecule, a virus or a cell before the sample explodes and turns into a plasma. Here we report the first experimental demonstration of this principle using the FLASH soft-X-ray free-electron laser. An intense 25 fs, 4 x 10(13) W cm(-2) pulse, containing 10(12) photons at 32 nm wavelength, produced a coherent diffraction pattern from a nanostructured non-periodic object, before destroying it at 60,000 K. A novel X-ray camera assured single-photon detection sensitivity by filtering out parasitic scattering and plasma radiation. The reconstructed image, obtained directly from the coherent pattern by phase retrieval through oversampling(5-9), shows no measurable damage, and is reconstructed at the diffraction-limited resolution. A three-dimensional data set may be assembled from such images when copies of a reproducible sample are exposed to the beam one by one(10).
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| 46. |
- Chapman, Henry N, et al.
(författare)
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Femtosecond time-delay X-ray holography
- 2007
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 448:7154, s. 676-679
-
Tidskriftsartikel (refereegranskat)abstract
- Extremely intense and ultrafast X-ray pulses from free-electron lasers offer unique opportunities to study fundamental aspects of complex transient phenomena in materials. Ultrafast time-resolved methods usually require highly synchronized pulses to initiate a transition and then probe it after a precisely defined time delay. In the X-ray regime, these methods are challenging because they require complex optical systems and diagnostics. Here we propose and apply a simple holographic measurement scheme, inspired by Newton's 'dusty mirror' experiment1, to monitor the X-ray-induced explosion of microscopic objects. The sample is placed near an X-ray mirror; after the pulse traverses the sample, triggering the reaction, it is reflected back onto the sample by the mirror to probe this reaction. The delay is encoded in the resulting diffraction pattern to an accuracy of one femtosecond, and the structural change is holographically recorded with high resolution. We apply the technique to monitor the dynamics of polystyrene spheres in intense free-electron-laser pulses, and observe an explosion occurring well after the initial pulse. Our results support the notion that X-ray flash imaging2, 3 can be used to achieve high resolution, beyond radiation damage limits for biological samples4. With upcoming ultrafast X-ray sources we will be able to explore the three-dimensional dynamics of materials at the timescale of atomic motion.
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| 47. |
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| 48. |
- Exbrayat, J. -F, et al.
(författare)
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Ensemble modelling of nitrogen fluxes : Data fusion for a Swedish meso-scale catchment
- 2010
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1607-7938 .- 1027-5606. ; 14:12, s. 2383-2397
-
Tidskriftsartikel (refereegranskat)abstract
- Model predictions of biogeochemical fluxes at the landscape scale are highly uncertain, both with respect to stochastic (parameter) and structural uncertainty. In this study 5 different models (LASCAM, LASCAM-S, a selfdeveloped tool, SWAT and HBV-N-D) designed to simulate hydrological fluxes as well as mobilisation and transport of one or several nitrogen species were applied to the mesoscale River Fyris catchment in mid-eastern Sweden. Hydrological calibration against 5 years of recorded daily discharge at two stations gave highly variable results with Nash-Sutcliffe Efficiency (NSE) ranging between 0.48 and 0.83. Using the calibrated hydrological parameter sets, the parameter uncertainty linked to the nitrogen parameters was explored in order to cover the range of possible predictions of exported loads for 3 nitrogen species: nitrate (NO3), ammonium (NH4) and total nitrogen (Tot-N). For each model and each nitrogen species, predictions were ranked in two different ways according to the performance indicated by two different goodness-of-fit measures: the coefficient of determination R2 and the root mean square error RMSE. A total of 2160 deterministic Single Model Ensembles (SME) was generated using an increasing number of members (from the 2 best to the 10 best single predictions). Finally the best SME for each model, nitrogen species and discharge station were selected and merged into 330 different Multi-Model Ensembles (MME). The evolution of changes in R2 and RMSE was used as a performance descriptor of the ensemble procedure. In each studied case, numerous ensemble merging schemes were identified which outperformed any of their members. Improvement rates were generally higher when worse members were introduced. The highest improvements were achieved for the nitrogen SMEs compiled with multiple linear regression models with R2 selected members, which resulted in the RMSE decreasing by up to 90%. © Author(s) 2010.
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| 49. |
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| 50. |
- Exbrayat, J. F., et al.
(författare)
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Multi-model data fusion as a tool for PUB : example in a Swedish mesoscale catchment
- 2011
-
Ingår i: Advances in Geosciences. - : Copernicus Publications. - 1680-7340 .- 1680-7359. ; 29, s. 43-50
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Tidskriftsartikel (refereegranskat)abstract
- Post-processing the output of different rainfall-runoff models allows one to pool strengths of each model to produce more reliable predictions. As a new approach in the frame of the "Prediction in Ungauged Basins" initiative, this study investigates the geographical transferability of different parameter sets and data-fusion methods which were applied to 5 different rainfall-runoff models for a low-land catchment in Central Sweden. After usual calibration, we adopted a proxy-basin validation approach between two similar but non-nested sub-catchments in order to simulate ungauged conditions. Many model combinations outperformed the best single model predictions with improvements of efficiencies from 0.70 for the best single model predictions to 0.77 for the best ensemble predictions. However no "best" data-fusion method could be determined as similar performances were obtained with different merging schemes. In general, poorer model performance, i.e. lower efficiency, was less likely to occur for ensembles which included more individual models.
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