| 1. |
- Kunnus, Kristjan, et al.
(författare)
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A setup for resonant inelastic soft x-ray scattering on liquids at free electron laser light sources
- 2012
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 83:12
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Tidskriftsartikel (refereegranskat)abstract
- We present a flexible and compact experimental setup that combines an in vacuum liquid jet with an x-ray emission spectrometer to enable static and femtosecond time-resolved resonant inelastic soft x-ray scattering (RIXS) measurements from liquids at free electron laser (FEL) light sources. We demonstrate the feasibility of this type of experiments with the measurements performed at the Linac Coherent Light Source FEL facility. At the FEL we observed changes in the RIXS spectra at high peak fluences which currently sets a limit to maximum attainable count rate at FELs. The setup presented here opens up new possibilities to study the structure and dynamics in liquids. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4772685]
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| 2. |
- Bergström, Lars, et al.
(författare)
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Investigating gamma ray lines from dark matter with future observatories
- 2012
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :11, s. 025-
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Tidskriftsartikel (refereegranskat)abstract
- We study the prospects for studying line features in gamma-ray spectra with upcoming gamma-ray experiments, such as HESS-II, the Cherenkov Telescope Array (CTA), and the GAMMA-400 satellite. As an example we use the narrow feature at 130 GeV seen in public data from the Fermi-LAT satellite. We found that all three experiments should be able to confidently confirm or rule out the presence of this 130 GeV feature. If it is real, it should be confirmed with a confidence level higher than 5 sigma. Assuming it to be a spectral signature of dark matter origin, GAMMA-400, thanks to a projected energy resolution of about 1.5 % at 100 GeV, should also be able to resolve both the gamma gamma line and a corresponding Z gamma or H gamma feature, if the corresponding branching ratio is comparable to that into two photons. It will also allow to distinguish between a gamma-ray line and the similar feature resulting from internal bremsstrahlung photons.
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| 3. |
- Coogan, Adam, et al.
(författare)
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Efficient gravitational wave template bank generation with differentiable waveforms
- 2022
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 106:12
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Tidskriftsartikel (refereegranskat)abstract
- The most sensitive search pipelines for gravitational waves from compact binary mergers use matched filters to extract signals from the noisy data stream coming from gravitational wave detectors. Matched-filter searches require banks of template waveforms covering the physical parameter space of the binary system. Unfortunately, template bank construction can be a time-consuming task. Here we present a new method for efficiently generating template banks that utilizes automatic differentiation to calculate the parameter space metric. Principally, we demonstrate that automatic differentiation enables accurate computation of the metric for waveforms currently used in search pipelines, whilst being computationally cheap. Additionally, by combining random template placement and a Monte Carlo method for evaluating the fraction of the parameter space that is currently covered, we show that search-ready template banks for frequency-domain waveforms can be rapidly generated. Finally, we argue that differentiable waveforms offer a pathway to accelerating stochastic placement algorithms. We implement all our methods into an easy-to-use python package based on the jax framework, diffbank, to allow the community to easily take advantage of differentiable waveforms for future searches.
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| 4. |
- Höbig, Nicole, et al.
(författare)
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Lake Banyoles (northeastern Spain) : A Last Glacial to Holocene multi-proxy study with regard to environmental variability and human occupation
- 2012
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Ingår i: Quaternary International. - Oxford : Elsevier. - 1040-6182 .- 1873-4553. ; 274, s. 205-218
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Tidskriftsartikel (refereegranskat)abstract
- Analyses of a 67-m long sediment core from Lake Banyoles (northeastern Spain) have revealed evidence for the palaeoclimate history of the northern Iberian Peninsula. Investigations have included high-resolution and non-destructive sediment-physical, geochemical, and optical methods to generate proxies indicative of sedimentologic variability and climate change. Primary stratigraphic control is based on C-14 and U-series dates of organic and inorganic material, as well as tephra from the Late Pleistocene Olot volcanic episode. While preliminary ages obtained for the core base date back to approximately 60 ka, the Last Glacial Maximum (23-19 ka) interval ends at 15 m. The top 8 m of deposits accumulated in the Holocene. Several slump events were observed in the core section, as were microtectonic structures, which constrain the movement. Evidence for palaeoclimate variations in element ratios is interpreted to represent effects of Heinrich Events H0-H5. Associated changes in environmental conditions (e.g., humidity) may have affected human occupation during the Palaeolithic-Neolithic period. Implications on human occupation in northeastern Iberia due to climate changes are discussed from archeological findings and cave sediments in neighboring areas and are analyzed with respect to the palaeolimnologic of lake Banyoles. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.
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| 5. |
- Kubin, Markus, et al.
(författare)
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Soft x-ray absorption spectroscopy of metalloproteins and high-valent metal-complexes at room temperature using free-electron lasers
- 2017
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Ingår i: Structural Dynamics. - : AMER INST PHYSICS. - 2329-7778. ; 4:5
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption spectroscopy at the L-edge of 3d transition metals provides unique information on the local metal charge and spin states by directly probing 3d-derived molecular orbitals through 2p-3d transitions. However, this soft x-ray technique has been rarely used at synchrotron facilities for mechanistic studies of metalloenzymes due to the difficulties of x-ray-induced sample damage and strong background signals from light elements that can dominate the low metal signal. Here, we combine femtosecond soft x-ray pulses from a free-electron laser with a novel x-ray fluorescence-yield spectrometer to overcome these difficulties. We present L-edge absorption spectra of inorganic high-valent Mn complexes (Mn similar to 6-15 mmol/l) with no visible effects of radiation damage. We also present the first L-edge absorption spectra of the oxygen evolving complex (Mn4CaO5) in Photosystem II (Mn < 1 mmol/l) at room temperature, measured under similar conditions. Our approach opens new ways to study metalloenzymes under functional conditions. (C) 2017 Author(s).
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| 6. |
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| 7. |
- Mitzner, Rolf, et al.
(författare)
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L-Edge X-ray Absorption Spectroscopy of Dilute Systems Relevant to Metalloproteins Using an X-ray Free-Electron Laser
- 2013
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:21, s. 3641-3647
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Tidskriftsartikel (refereegranskat)abstract
- L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming 0 K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples.
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| 8. |
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| 9. |
- Schröder, Henning, et al.
(författare)
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Varying photo-dissociation mechanisms in Fe(CO)5 and Cr(CO)6 from femtosecond valence photoemission and excited-state moleculardynamics simulations
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present measured and calculated time-resolved photoelectron spectra of photoexcited gas-phase Fe(CO)5 and Cr(CO)6. Upon electronic excitation with 266 nm pump pulses and by probing with 23 eV photons from a femtosecond high-order har-monic generation source, we observe differences between Fe(CO)5 and Cr(CO)6 that indicate that the excited-state and dissociation dynamics are slower in Fe(CO)5 than in Cr(CO)6. Changing photoelectron intensities and binding energies combined with excited-state molecular dynamics simulations indicate repopulations of excited states from bound excited to dissociative excited states and to the dissociated species. We find that the more open and flexible structure of Fe(CO)5 with larger metal-carbonyl angles enables the photoexcited states of Fe(CO)5 to dissipate energy by angular distortions as observed in longer populations of bound excited states. The more compactand closed structure of Cr(CO)6 does not enable this relaxation resulting in fasterdissociation.
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| 10. |
- Wernet, Philippe, et al.
(författare)
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Mapping chemical bonding of reaction intermediates with femtosecond X-ray laser spectroscopy
- 2013
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Ingår i: XVIIIth International Conference on Ultrafast Phenomena. - : EDP Sciences. - 9782759809561 ; , s. 05025-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We determine the pathways in the photo-dissociation reactions of Fe(CO)5 both in the gas phase and in solution by mapping the valence electronic structure of the reaction intermediates with femtosecond X-ray laser spectroscopy.
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