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- Schmising, Clemens von Korff, et al.
(author)
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Element-Specific Magnetization Dynamics of Complex Magnetic Systems Probed by Ultrafast Magneto-Optical Spectroscopy
- 2020
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In: Applied Sciences. - : MDPI AG. - 2076-3417. ; 10:21
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Journal article (peer-reviewed)abstract
- The vision to manipulate and control magnetism with light is driven on the one hand by fundamental questions of direct and indirect photon-spin interactions, and on the other hand by the necessity to cope with ever growing data volumes, requiring radically new approaches on how to write, read and process information. Here, we present two complementary experimental geometries to access the element-specific magnetization dynamics of complex magnetic systems via ultrafast magneto-optical spectroscopy in the extreme ultraviolet spectral range. First, we employ linearly polarized radiation of a free electron laser facility to demonstrate decoupled dynamics of the two sublattices of an FeGd alloy, a prerequisite for all-optical magnetization switching. Second, we use circularly polarized radiation generated in a laboratory-based high harmonic generation setup to show optical inter-site spin transfer in a CoPt alloy, a mechanism which only very recently has been predicted to mediate ultrafast metamagnetic phase transitions.
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| 4. |
- Buck, Holly Jean, et al.
(author)
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Why residual emissions matter right now
- 2023
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In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-6798 .- 1758-678X. ; 13:4, s. 351-358
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Journal article (peer-reviewed)abstract
- Net-zero targets imply that continuing residual emissions will be balanced by carbon dioxide removal. However, residual emissions are typically not well defined, conceptually or quantitatively. We analysed governments’ long-term strategies submitted to the UNFCCC to explore projections of residual emissions, including amounts and sectors. We found substantial levels of residual emissions at net-zero greenhouse gas emissions, on average 18% of current emissions for Annex I countries. The majority of strategies were imprecise about which sectors residual emissions would originate from, and few offered specific projections of how residual emissions could be balanced by carbon removal. Our findings indicate the need for a consistent definition of residual emissions, as well as processes that standardize and compare expectations about residual emissions across countries. This is necessary for two reasons: to avoid projections of excessive residuals and correspondent unsustainable or unfeasible carbon-removal levels and to send clearer signals about the temporality of fossil fuel use.
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- Engel, Robin Y., et al.
(author)
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Electron population dynamics in resonant non-linear x-ray absorption in nickel at a free-electron laser
- 2023
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In: Structural Dynamics. - : American Institute of Physics (AIP). - 2329-7778. ; 10:5
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Journal article (peer-reviewed)abstract
- Free-electron lasers provide bright, ultrashort, and monochromatic x-ray pulses, enabling novel spectroscopic measurements not only with femtosecond temporal resolution: The high fluence of their x-ray pulses can also easily enter the regime of the non-linear x-ray-matter interaction. Entering this regime necessitates a rigorous analysis and reliable prediction of the relevant non-linear processes for future experiment designs. Here, we show non-linear changes in the L-3-edge absorption of metallic nickel thin films, measured with fluences up to 60 J/cm(2). We present a simple but predictive rate model that quantitatively describes spectral changes based on the evolution of electronic populations within the pulse duration. Despite its simplicity, the model reaches good agreement with experimental results over more than three orders of magnitude in fluence, while providing a straightforward understanding of the interplay of physical processes driving the non-linear changes. Our findings provide important insights for the design and evaluation of future high-fluence free-electron laser experiments and contribute to the understanding of non-linear electron dynamics in x-ray absorption processes in solids at the femtosecond timescale.
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| 7. |
- Hans, Andreas, et al.
(author)
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Suppression of X-ray-Induced Radiation Damage to Biomolecules in Aqueous Environments by Immediate Intermolecular Decay of Inner-Shell Vacancies
- 2021
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 12:30, s. 7146-7150
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Journal article (peer-reviewed)abstract
- The predominant reason for the damaging power of high-energy radiation is multiple ionization of a molecule, either direct or via the decay of highly excited intermediates, as, e.g., in the case of X-ray irradiation. Consequently, the molecule is irreparably damaged by the subsequent fragmentation in a Coulomb explosion. In an aqueous environment, however, it has been observed that irradiated molecules may be saved from fragmentation presumably by charge and energy dissipation mechanisms. Here, we show that the protective effect of the environment sets in even earlier than hitherto expected, namely immediately after single inner-shell ionization. By combining coincidence measurements of the fragmentation of X-ray-irradiated microsolvated pyrimidine molecules with theoretical calculations, we identify direct intermolecular electronic decay as the protective mechanism, outrunning the usually dominant Auger decay. Our results demonstrate that such processes play a key role in charge delocalization and have to be considered in investigations and models on high-energy radiation damage in realistic environments.
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| 8. |
- Lund, Jens Friis, et al.
(author)
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Net zero and the unexplored politics of residual emissions
- 2023
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In: Energy Research & Social Science. - : Elsevier BV. - 2214-6326 .- 2214-6296. ; 98:April
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Journal article (peer-reviewed)abstract
- In this perspective article, we call for more engagement with the unexplored politics of residual emissions. Residual emissions are those emissions that remain at the point of net zero, despite abatement efforts. Unlike carbon dioxide removal, which has been the focus of a lively research and policy debate, the notion of residual emissions remains relatively unexplored so far. With the mainstreaming of net zero as the long-term goal of climate policy, the politics of residual emissions are set to become a key point of contestation. Claims about residual emissions tend to revolve around notions of necessity and possibility, i.e. emissions that derive from activities deemed socially necessary yet impossible to fully abate. In this perspective article, we highlight how such claims are socially constructed and ultimately contingent on values, norms and interests. We call upon researchers to help render visible the geographically and historically contingent claims to necessity and possibility that underpin projected residual emissions. We see this as an important means to repoliticize debates about the limits and possibilities of emissions abatement, and suggest entry points for such research efforts.
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| 10. |
- Reich, Martin M., et al.
(author)
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Progressive gait ataxia following deep brain stimulation for essential tremor: adverse effect or lack of efficacy?
- 2016
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In: Brain. - : OXFORD UNIV PRESS. - 0006-8950 .- 1460-2156. ; 139, s. 2948-2956
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Journal article (peer-reviewed)abstract
- Thalamic deep brain stimulation is a mainstay treatment for severe and drug-refractory essential tremor, but postoperative management may be complicated in some patients by a progressive cerebellar syndrome including gait ataxia, dysmetria, worsening of intention tremor and dysarthria. Typically, this syndrome manifests several months after an initially effective therapy and necessitates frequent adjustments in stimulation parameters. There is an ongoing debate as to whether progressive ataxia reflects a delayed therapeutic failure due to disease progression or an adverse effect related to repeated increases of stimulation intensity. In this study we used a multimodal approach comparing clinical stimulation responses, modelling of volume of tissue activated and metabolic brain maps in essential tremor patients with and without progressive ataxia to disentangle a disease-related from a stimulation-induced aetiology. Ten subjects with stable and effective bilateral thalamic stimulation were stratified according to the presence ( five subjects) of severe chronic-progressive gait ataxia. We quantified stimulated brain areas and identified the stimulation- induced brain metabolic changes by multiple 18 F-fluorodeoxyglucose positron emission tomography performed with and without active neurostimulation. Three days after deactivating thalamic stimulation and following an initial rebound of symptom severity, gait ataxia had dramatically improved in all affected patients, while tremor had worsened to the presurgical severity, thus indicating a stimulation rather than disease-related phenomenon. Models of the volume of tissue activated revealed a more ventrocaudal stimulation in the ( sub) thalamic area of patients with progressive gait ataxia. Metabolic maps of both patient groups differed by an increased glucose uptake in the cerebellar nodule of patients with gait ataxia. Our data suggest that chronic progressive gait ataxia in essential tremor is a reversible cerebellar syndrome caused by a maladaptive response to neurostimulation of the ( sub) thalamic area. The metabolic signature of progressive gait ataxia is an activation of the cerebellar nodule, which may be caused by inadvertent current spread and antidromic stimulation of a cerebellar outflow pathway originating in the vermis. An anatomical candidate could be the ascending limb of the uncinate tract in the subthalamic area. Adjustments in programming and precise placement of the electrode may prevent this adverse effect and help fine-tuning deep brain stimulation to ameliorate tremor without negative cerebellar signs.
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