| 1. |
- George, H., et al.
(författare)
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Estimating Inner Magnetospheric Radial Diffusion Using a Hybrid-Vlasov Simulation
- 2022
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Ingår i: Frontiers in Astronomy and Space Sciences. - : Frontiers Media S.A.. - 2296-987X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Radial diffusion coefficients quantify non-adiabatic transport of energetic particles by electromagnetic field fluctuations in planetary radiation belts. Theoretically, radial diffusion occurs for an ensemble of particles that experience irreversible violation of their third adiabatic invariant, which is equivalent to a change in their Roederer L* parameter. Thus, the Roederer L* coordinate is the fundamental quantity from which radial diffusion coefficients can be computed. In this study, we present a methodology to calculate the Lagrangian derivative of L* from global magnetospheric simulations, and test it with an application to Vlasiator, a hybrid-Vlasov model of near-Earth space. We use a Hamiltonian formalism for particles confined to closed drift shells with conserved first and second adiabatic invariants to compute changes in the guiding center drift paths due to electric and magnetic field fluctuations. We investigate the feasibility of this methodology by computing the time derivative of L* for an equatorial ultrarelativistic electron population travelling along four guiding center drift paths in the outer radiation belt during a 5 minute portion of a Vlasiator simulation. Radial diffusion in this simulation is primarily driven by ultralow frequency waves in the Pc3 range (10-45 s period range) that are generated in the foreshock and transmitted through the magnetopause to the outer radiation belt environment. Our results show that an alternative methodology to compute detailed radial diffusion transport is now available and could form the basis for comparison studies between numerical and observational measurements of radial transport in the Earth's radiation belts.
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| 2. |
- Alho, M., et al.
(författare)
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Electron Signatures of Reconnection in a Global eVlasiator Simulation
- 2022
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 49:14
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Tidskriftsartikel (refereegranskat)abstract
- Geospace plasma simulations have progressed toward more realistic descriptions of the solar wind-magnetosphere interaction from magnetohydrodynamic to hybrid ion-kinetic, such as the state-of-the-art Vlasiator model. Despite computational advances, electron scales have been out of reach in a global setting. eVlasiator, a novel Vlasiator submodule, shows for the first time how electromagnetic fields driven by global hybrid-ion kinetics influence electrons, resulting in kinetic signatures. We analyze simulated electron distributions associated with reconnection sites and compare them with Magnetospheric Multiscale (MMS) spacecraft observations. Comparison with MMS shows that key electron features, such as reconnection inflows, heated outflows, flat-top distributions, and bidirectional streaming, are in remarkable agreement. Thus, we show that many reconnection-related features can be reproduced despite strongly truncated electron physics and an ion-scale spatial resolution. Ion-scale dynamics and ion-driven magnetic fields are shown to be significantly responsible for the environment that produces electron dynamics observed by spacecraft in near-Earth plasmas.
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| 3. |
- Dubart, M., et al.
(författare)
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Sub-grid modeling of pitch-angle diffusion for ion-scale waves in hybrid-Vlasov simulations with Cartesian velocity space
- 2022
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 29:10
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Tidskriftsartikel (refereegranskat)abstract
- Numerical simulations have grown to play a central role in modern sciences over the years. The ever-improving technology of supercomputers has made large and precise models available. However, this accuracy is often limited by the cost of computational resources. Lowering the simulation's spatial resolution in order to conserve resources can lead to key processes being unresolved. We have shown in a previous study how insufficient spatial resolution of the proton cyclotron instability leads to a misrepresentation of ion dynamics in hybrid-Vlasov simulations. This leads to larger than expected temperature anisotropy and loss-cone shaped velocity distribution functions. In this study, we present a sub-grid numerical model to introduce pitch-angle diffusion in a 3D Cartesian velocity space, at a spatial resolution where the relevant wave-particle interactions were previously not correctly resolved. We show that the method is successfully able to isotropize loss-cone shaped velocity distribution functions, and that this method could be applied to simulations in order to save computational resources and still correctly model wave-particle interactions.
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| 4. |
- Suni, J., et al.
(författare)
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Connection Between Foreshock Structures and the Generation of Magnetosheath Jets : Vlasiator Results
- 2021
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:20
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Tidskriftsartikel (refereegranskat)abstract
- Earth's magnetosheath consists of shocked solar wind plasma that has been compressed and slowed down at the Earth's bow shock. Magnetosheath jets are pulses of enhanced dynamic pressure in the magnetosheath. Jets have been observed by numerous spacecraft missions, but their origin has remained unconfirmed, though several formation mechanisms have been suggested. In this study, we use a method for automatically identifying and tracking jets as well as foreshock compressive structures (FCSs) in four 2D runs of the global hybrid-Vlasov simulation Vlasiator. We find that up to 75% of magnetosheath jets are caused by FCSs impacting the bow shock. These jets propagate deeper into the magnetosheath than the remaining 25% of jets that are not caused by FCSs. We conduct a visual case study of one jet that was not caused by FCSs and find that the bow shock was not rippled before the formation of the jet. Plain Language Summary The space around Earth is filled with plasma, the fourth state of matter. Earth's magnetic field shields our planet from the stream of plasma coming from the Sun, the solar wind. The solar wind plasma is slowed down at the Earth's bow shock, before it flows against and around the Earth's magnetic field in the magnetosheath. Sometimes, pulses of high density or velocity can occur in the magnetosheath that have the potential to disturb the inner regions of near-Earth space where many spacecraft orbit. We call these pulses magnetosheath jets. Magnetosheath jets have been observed by many spacecraft over the past few decades, but how they form has remained unclear. In this study, we use the Vlasiator model to simulate plasma in near-Earth space and investigate the origins of magnetosheath jets. We find that the formation of up to 75% of these jets can be explained by compressive structures in the foreshock, a region populated by intense wave activity extending sunward of the quasi-parallel bow shock, where interplanetary magnetic field lines allow shock-reflected particles to travel back toward the Sun. Key Points We investigated magnetosheath jets in four hybrid-Vlasov simulation runs with different solar wind parameters Foreshock compressive structures can explain the formation of up to 75% of magnetosheath jets The foreshock compressive structure-caused jets travel deeper into the magnetosheath than the 25% of the jets whose origins remain unclear
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| 5. |
- Correa, J., et al.
(författare)
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The PERCIVAL detector : first user experiments
- 2023
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 30, s. 242-250
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Tidskriftsartikel (refereegranskat)abstract
- The PERCIVAL detector is a CMOS imager designed for the soft X-ray regime at photon sources. Although still in its final development phase, it has recently seen its first user experiments: ptychography at a free-electron laser, holographic imaging at a storage ring and preliminary tests on X-ray photon correlation spectroscopy. The detector performed remarkably well in terms of spatial resolution achievable in the sample plane, owing to its small pixel size, large active area and very large dynamic range; but also in terms of its frame rate, which is significantly faster than traditional CCDs. In particular, it is the combination of these features which makes PERCIVAL an attractive option for soft X-ray science.
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| 6. |
- Johlander, Andreas, 1990-, et al.
(författare)
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Ion Acceleration Efficiency at the Earth's Bow Shock : Observations and Simulation Results
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 914:2
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Tidskriftsartikel (refereegranskat)abstract
- Collisionless shocks are some of the most efficient particle accelerators in heliospheric and astrophysical plasmas. Here we study and quantify ion acceleration at Earth's bow shock with observations from NASA's Magnetospheric Multiscale (MMS) satellites and in a global hybrid-Vlasov simulation. From the MMS observations, we find that quasiparallel shocks are more efficient at accelerating ions. There, up to 15% of the available energy goes into accelerating ions above 10 times their initial energy. Above a shock-normal angle of similar to 50 degrees, essentially no energetic ions are observed downstream of the shock. We find that ion acceleration efficiency is significantly lower when the shock has a low Mach number (M ( A ) < 6) while there is little Mach number dependence for higher values. We also find that ion acceleration is lower on the flanks of the bow shock than at the subsolar point regardless of the Mach number. The observations show that a higher connection time of an upstream field line leads to somewhat higher acceleration efficiency. To complement the observations, we perform a global hybrid-Vlasov simulation with realistic solar-wind parameters with the shape and size of the bow shock. We find that the ion acceleration efficiency in the simulation shows good quantitative agreement with the MMS observations. With the combined approach of direct spacecraft observations, we quantify ion acceleration in a wide range of shock angles and Mach numbers.
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| 7. |
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| 8. |
- Palmroth, M., et al.
(författare)
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Magnetosheath jet properties and evolution as determined by a global hybrid-Vlasov simulation
- 2018
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 36:5, s. 1171-1182
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Tidskriftsartikel (refereegranskat)abstract
- We use a global hybrid-Vlasov simulation for the magnetosphere, Vlasiator, to investigate magnetosheath high-speed jets. Unlike many other hybrid-kinetic simulations, Vlasiator includes an unscaled geomagnetic dipole, indicating that the simulation spatial and temporal dimensions can be given in SI units without scaling. Thus, for the first time, this allows investigating the magnetosheath jet properties and comparing them directly with the observed jets within the Earth's magnetosheath. In the run shown in this paper, the interplanetary magnetic field (IMF) cone angle is 30°, and a foreshock develops upstream of the quasi-parallel magnetosheath. We visually detect a structure with high dynamic pressure propagating from the bow shock through the magnetosheath. The structure is confirmed as a jet using three different criteria, which have been adopted in previous observational studies. We compare these criteria against the simulation results. We find that the magnetosheath jet is an elongated structure extending earthward from the bow shock by ∼ 2.6 RE, while its size perpendicular to the direction of propagation is ∼ 0.5R/E. We also investigate the jet evolution and find that the jet originates due to the interaction of the bow shock with a high-dynamic-pressure structure that reproduces observational features associated with a short, large-amplitude magnetic structure (SLAMS). The simulation shows that magnetosheath jets can develop also under steady IMF, as inferred by observational studies. To our knowledge, this paper therefore shows the first global kinetic simulation of a magnetosheath jet, which is in accordance with three observational jet criteria and is caused by a SLAMS advecting towards the bow shock.
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| 9. |
- Schmising, C. von Korff, et al.
(författare)
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Imaging Ultrafast Demagnetization Dynamics after a Spatially Localized Optical Excitation
- 2014
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Ingår i: Physical Review Letters. - 1079-7114. ; 111:21
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Tidskriftsartikel (refereegranskat)abstract
- Ultrashort, coherent x-ray pulses of a free-electron laser are used to holographically image the magnetization dynamics within a magnetic domain pattern after creation of a localized excitation via an optical standing wave. We observe a spatially confined reduction of the magnetization within a couple of hundred femtoseconds followed by its slower recovery. Additionally, the experimental results show evidence of a spatial evolution of magnetization, which we attribute to ultrafast transport of nonequilibrium spin-polarized electrons for early times and to a fluence-dependent remagnetization rate for later times.
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| 10. |
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| 11. |
- Turc, L., et al.
(författare)
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Transmission of foreshock waves through Earth's bow shock
- 2023
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Ingår i: Nature Physics. - : Springer Nature. - 1745-2473 .- 1745-2481. ; 19:1, s. 78-86
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Tidskriftsartikel (refereegranskat)abstract
- The Earth's magnetosphere and its bow shock, which is formed by the interaction of the supersonic solar wind with the terrestrial magnetic field, constitute a rich natural laboratory enabling in situ investigations of universal plasma processes. Under suitable interplanetary magnetic field conditions, a foreshock with intense wave activity forms upstream of the bow shock. So-called 30 s waves, named after their typical period at Earth, are the dominant wave mode in the foreshock and play an important role in modulating the shape of the shock front and affect particle reflection at the shock. These waves are also observed inside the magnetosphere and down to the Earth's surface, but how they are transmitted through the bow shock remains unknown. By combining state-of-the-art global numerical simulations and spacecraft observations, we demonstrate that the interaction of foreshock waves with the shock generates earthward-propagating, fast-mode waves, which reach the magnetosphere. These findings give crucial insight into the interaction of waves with collisionless shocks in general and their impact on the downstream medium.
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| 12. |
- von Korff Schmising, C., et al.
(författare)
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Imaging Non-Local Magnetization Dynamics
- 2016
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Ingår i: Synchrotron Radiation News. - : Informa UK Limited. - 0894-0886 .- 1931-7344. ; 29:3, s. 26-31
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Tidskriftsartikel (refereegranskat)abstract
- Many fundamental processes in magnetism take place on a nanometer length and sub-picosecond time scale. An important example of such phenomena in magnetism is ultrafast, spin-polarized transport of laser-excited hot electrons, which is now being recognized as playing a crucial role for novel spintronic devices and for optically induced magnetic switching. Recent experimental examples include the demonstration of all-optical helicity dependent control of spin-polarized currents at interfaces [1], the design of novel and efficient terahertz emitters [2], and nanoscale spin reversal in chemically heterogeneous GdFeCo driven by non-local transfer of angular momentum [3]. In particular, for advanced information technologies with bit densities already exceeding 1 terabit per square inch with bit cell dimensions of (15 × 38 nm2) [4], it is of fundamental importance to understand and eventually control the mechanisms responsible for optically induced spin dynamics on the nanoscale.
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| 13. |
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| 14. |
- Hoilijoki, S., et al.
(författare)
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Properties of Magnetic Reconnection and FTEs on the Dayside Magnetopause With and Without Positive IMF Bx Component During Southward IMF
- 2019
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 124:6, s. 4037-4048
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes properties and behavior of magnetic reconnection and flux transfer events (FTEs) on the dayside magnetopause using the global hybrid-Vlasov code Vlasiator. We investigate two simulation runs with and without a sunward (positive)B-x component of the interplanetary magnetic field (IMF) when the IMF is southward. The runs are two-dimensional in real space in the noon-midnight meridional (polar) plane and three-dimensional in velocity space. Solar wind input parameters are identical in the two simulations with the exception that the IMF is purely southward in one but tilted 45 degrees toward the Sun in the other. In the purely southward case (i.e., without B-x) the magnitude of the magnetos heath magnetic field component tangential to the magnetopause is larger than in the run with a sunward tilt. This is because the shock normal is perpendicular to the IMF at the equatorial plane, whereas in the other run the shock configuration is oblique and a smaller fraction of the total IMF strength is compressed at the shock crossing. Hence, the measured average and maximum reconnection rate are larger in the purely southward run. The run with tilted IMF also exhibits a north-south asymmetry in the tangential magnetic field caused by the different angle between the IMF and the bow shock normal north and south of the equator. Greater north-south asymmetries are seen in the FTE occurrence rate, size, and velocity as well; FTEs moving toward the Southern Hemisphere are larger in size and observed less frequently than FTEs in the Northern Hemisphere.
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| 15. |
- Kozlowska, K., et al.
(författare)
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Patterns of healthy lifestyle and positive health attitudes in older Europeans
- 2008
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Ingår i: The Journal of Nutrition, Health & Aging. - 1279-7707 .- 1760-4788. ; 12:10, s. 728-733
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: To determine (i) the extent to which recommended lifestyle healthy behaviors are adopted and the existence of positive attitudes to health; (ii) the relative influence of socio-demographic variables on multiple healthy lifestyle behaviors and positive attitudes to health; (iii) the association between healthy lifestyle behaviors and positive attitudes to health. Design: two distinct healthy behavioral measures were developed: (i) healthy lifestyles based on physical activity, no cigarette smoking, no/moderate alcohol drinking, maintaining a "healthy" weight and having no sleeping problems and (ii) positive health attitudes based on having positive emotional attitudes, such as: self-perceived good health status, being calm, peaceful and happy for most of the time, not expecting health to get worse and regular health check-ups. A composite healthy lifestyle index, ranging from 0 (none of behaviors met) to 5 (all behaviors met) was calculated by summing up the individual's scores for the five healthy lifestyle items. Afterwards, each individual's index was collapsed into three levels: 0-2 equivalent to 'level 1' (subjectively regarded as 'too low'), a score of 3 equivalent to 'level 2' ('fair') and 4-5 as 'level 3' satisfactory 'healthy lifestyle' practices. The same procedure was applied to the positive health attitudes index. Multinomial logistic regression analyses by a forward selection procedure were used to calculate the adjusted odds ratio (OR) with 95% confidence interval (95% CI). Participants: a multi-national sample consisting of 638 older Europeans from 8 countries, aged 65-74 and 75+, living alone or with others. Results and conclusions: maintaining a "healthy" weight was the most frequently cited factor in the healthy lifestyles index and therefore assumed to be the most important to the older Europeans in the study; positive attitudes to health were relatively low; participants achieved a 'satisfactory' level for healthy lifestyles index (level 3) more frequently than a satisfactory level for positive attitudes to health; having a satisfactory 'healthy lifestyle' was directly related to having a satisfactory level of positive attitudes to health based on the positive health attitudes index; income and geographical location in Europe appeared to be key predictors for meeting both the recommended healthy lifestyle factors in the index and having positive health attitudes however, the composition and nature of the study sample should be taken into consideration when considering the impact of the location on healthy lifestyles and attitudes to health across Europe.
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| 16. |
- Engel, Robin Y., et al.
(författare)
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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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Ingår i: Structural Dynamics. - : American Institute of Physics (AIP). - 2329-7778. ; 10:5
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Tidskriftsartikel (refereegranskat)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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| 17. |
- Geilhufe, J., et al.
(författare)
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Extracting depth information of 3-dimensional structures from a single-view X-ray Fourier-transform hologram
- 2014
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Ingår i: Optics Express. - 1094-4087. ; 22:21, s. 24959-24969
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how information about the three-dimensional structure of an object can be extracted from a single Fourier-transform Xray hologram. In contrast to lens-based 3D imaging approaches that provide depth information of a specimen utilizing several images from different angles or via adjusting the focus to different depths, our method capitalizes on the use of the holographically encoded phase and amplitude information of the object's wavefield. It enables single-shot measurements of 3D objects at coherent X-ray sources. As the ratio of longitudinal resolution over transverse resolution scales proportional to the diameter of the reference beam aperture over the X-ray wavelength, we expect the approach to be particularly useful in the extreme ultraviolet and soft-X-ray regime. (C) 2014 Optical Society of America
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| 18. |
- Hennecke, Martin, et al.
(författare)
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Ultrafast opto-magnetic effects in the extreme ultraviolet spectral range
- 2024
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Ingår i: Communications Physics. - : Springer Nature. - 2399-3650. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect (IFE) are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism on timescales as short as the excitation pulse itself. As the IFE scales with the spin-orbit coupling strength of the involved electronic states, photo-exciting the strongly spin-orbit coupled core-level electrons in magnetic materials appears as an appealing method to transiently generate large opto-magnetic moments. Here, we investigate this scenario in a ferrimagnetic GdFeCo alloy by using intense and circularly polarized pulses of extreme ultraviolet radiation. Our results reveal ultrafast and strong helicity-dependent magnetic effects which are in line with the characteristic fingerprints of an IFE, corroborated by ab initio opto-magnetic IFE theory and atomistic spin dynamics simulations.
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| 19. |
- Höffner, Sebastian, et al.
(författare)
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Deep understanding of everyday activity commands for household robots
- 2022
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Ingår i: Semantic Web. - : IOS Press. - 1570-0844 .- 2210-4968. ; 13:5, s. 895-909
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Tidskriftsartikel (refereegranskat)abstract
- Going from natural language directions to fully specified executable plans for household robots involves a challenging variety of reasoning steps. In this paper, a processing pipeline to tackle these steps for natural language directions is proposed and implemented. It uses the ontological Socio-physical Model of Activities (SOMA) as a common interface between its components. The pipeline includes a natural language parser and a module for natural language grounding. Several reasoning steps formulate simulation plans, in which robot actions are guided by data gathered using human computation. As a last step, the pipeline simulates the given natural language direction inside a virtual environment. The major advantage of employing an overarching ontological framework is that its asserted facts can be stored alongside the semantics of directions, contextual knowledge, and annotated activity models in one central knowledge base. This allows for a unified and efficient knowledge retrieval across all pipeline components, providing flexibility and reasoning capabilities as symbolic knowledge is combined with annotated sub-symbolic models.
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| 20. |
- Kajdic, P., et al.
(författare)
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ULF Wave Transmission Across Collisionless Shocks : 2.5D Local Hybrid Simulations
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:11
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Tidskriftsartikel (refereegranskat)abstract
- We study the interaction of upstream ultralow frequency (ULF) waves with collisionless shocks by analyzing the outputs of 11 2D local hybrid simulation runs. Our simulated shocks have Alfvenic Mach numbers between 4.29 and 7.42 and their theta BN angles are 15 degrees, 30 degrees, 45 degrees, and 50 degrees. The ULF wave foreshocks develop upstream of all of them. The wavelength and the amplitude of the upstream waves exhibit a complex dependence on the shock's MA and theta BN. The wavelength positively correlates with both parameters, with the dependence on theta BN being much stronger. The amplitude of the ULF waves is proportional to the product of the reflected beam velocity and density, which also depend on MA and theta BN. The interaction of the ULF waves with the shock causes large-scale (several tens of upstream ion inertial lengths) shock rippling. The properties of the shock ripples are related to the ULF wave properties, namely their wavelength and amplitude. In turn, the ripples have a large impact on the ULF wave transmission across the shock because they change local shock properties (theta BN, strength), so that different sections of the same ULF wavefront encounter shock with different characteristics. Downstream fluctuations do not resemble the upstream waves in terms the wavefront extension, orientation or their wavelength. However, some features are conserved in the Fourier spectra of downstream compressive waves that present a bump or flattening at wavelengths approximately corresponding to those of the upstream ULF waves. In the transverse downstream spectra, these features are weaker.
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| 21. |
- Malm, Erik, et al.
(författare)
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Reference shape effects on Fourier transform holography
- 2022
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Ingår i: Optics Express. - 1094-4087. ; 30:21, s. 38424-38438
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Tidskriftsartikel (refereegranskat)abstract
- Soft-x-ray holography which utilizes an optics mask fabricated in direct contact with the sample, is a widely applied x-ray microscopy method, in particular, for investigating magnetic samples. The optics mask splits the x-ray beam into a reference wave and a wave to illuminate the sample. The reconstruction quality in such a Fourier-transform holography experiment depends primarily on the characteristics of the reference wave, typically emerging from a small, high-aspect-ratio pinhole in the mask. In this paper, we study two commonly used reference geometries and investigate how their 3D structure affects the reconstruction within an x-ray Fourier holography experiment. Insight into these effects is obtained by imaging the exit waves from reference pinholes via high-resolution coherent diffraction imaging combined with three-dimensional multislice simulations of the x-ray propagation through the reference pinhole. The results were used to simulate Fourier-transform holography experiments to determine the spatial resolution and precise location of the reconstruction plane for different reference geometries. Based on our findings, we discuss the properties of the reference pinholes with view on application in soft-x-ray holography experiments.
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| 22. |
- Persson-Sjodin, Emma, et al.
(författare)
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Withers vertical movement symmetry is useful for locating the primary lame limb in naturally occurring lameness
- 2024
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Ingår i: Equine Veterinary Journal. - : WILEY. - 0425-1644 .- 2042-3306. ; 56:1, s. 76-88
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundDuring orthopaedic assessment of lame horses, a head nod is commonly present in both primary forelimb and hindlimb lame horses. Additional motion metrics that could assist clinicians in correctly differentiating between these two scenarios would be of great clinical value. ObjectivesThe primary objective of this study was to examine whether withers movement asymmetry can be used in a clinical setting to distinguish primary forelimb lameness from compensatory head movement asymmetry due to primary hindlimb lameness. Study designRetrospective, multicentre study. MethodsMovement asymmetry of head, withers and pelvis was measured using multi-camera optical motion capture, as part of routine lameness investigations at four European equine hospitals. Vertical movement asymmetry parameters from 317 horses trotting in a straight line were compared before and after successful diagnostic analgesia of a single limb. Descriptive statistics, t-tests and linear models were used to analyse the data. ResultsIn forelimb lame horses, 80%-81% showed head and withers asymmetry both indicating lameness in the same forelimb. In hindlimb lame horses, 69%-72% showed head asymmetry ipsilateral to the lame hindlimb and withers asymmetry diagonal to the lame hindlimb, thus, head and withers asymmetry indicated lameness in different forelimbs. A large (>15 mm) compensatory head nod was seen in 28%-31% of the hindlimb lame horses. In 89%-92% of these, head and withers asymmetry indicated lameness in different forelimbs. Withers asymmetry decreased linearly with reduced head or pelvic asymmetry for both forelimb and hindlimb lame horses. Main limitationsCompensatory strategies were evaluated on group level to identify common patterns, potentially ignoring uncommon individual strategies. ConclusionsWithers vertical movement asymmetry metrics can be useful in helping to locate the primary lame limb during quantitative lameness assessment. Head and withers movement asymmetry parameters generally indicate the same forelimb in forelimb lame horses, but different forelimbs in hindlimb lame horses.
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| 23. |
- Pfau, Bastian, et al.
(författare)
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Influence of stray fields on the switching-field distribution for bit-patterned media based on pre-patterned substrates
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:13
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Tidskriftsartikel (refereegranskat)abstract
- Using a direct imaging method, we experimentally investigate the reversal of magnetic islands in a bit-patterned media sample based on a pre-patterned substrate. Due to systematic variation of the island distances in the media, we are able to study the influence of the dipolar interaction on the switching-field distribution of the island ensemble. The experimental findings are explained by an analytical magnetostatic model that allows us to quantify the different components of the demagnetizing field in the system and to distinguish intrinsic and dipolar broadening of the switching-field distribution. Besides the well-known dipolar broadening due to stray fields from neighboring islands, we find strong influence from the magnetized trench material on the island switching. (C) 2014 Author(s).
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| 24. |
- Stiel, H., et al.
(författare)
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2D and 3D Nanoscale Imaging Using High Repetition Rate Laboratory-Based Soft X-Ray Sources
- 2018
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Ingår i: X-Ray Lasers 2016 - Proceedings of the 15th International Conference on X-Ray Lasers. - Cham : Springer International Publishing. - 9783319730240 ; 202, s. 265-272
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Konferensbidrag (refereegranskat)abstract
- In this contribution, we report about tomographic nanoscale imaging using a laser-produced plasma-based laboratory transmission X-ray microscope (LTXM) in the water window. The soft X-ray radiation of the LTXM is provided by a high average power laser-produced (1.3 kHz repetition rate, 0.5 ns pulse duration, 140 W average power) plasma source, a multilayer condenser mirror, an objective zone plate, and a back-illuminated CCD camera as a detector. In the second part of the contribution, we will present recent results on holography and coherent diffraction imaging using our high repetition rate X-ray laser. We will discuss advantages of these methods and its potential for nanoscale imaging.
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| 25. |
- Turrini, Aida, et al.
(författare)
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The Informal Networks in Food Procurement by Older People : A Cross European Comparison
- 2010
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Ingår i: Ageing International. - : Springer. - 0163-5158 .- 1936-606X. ; 35:4, s. 253-275
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Tidskriftsartikel (refereegranskat)abstract
- Healthy dietary profiles contribute to successful aging, and dietary intake is dependent upon food procurement capabilities. Both formal and informal social networks can contribute to grocery shopping capabilities and methods of food procurement. This investigation explores the role of informal networks in food procurement methods among adults aged 65 years and older, and compares differences across eight European countries. Food shopping ways (FSW), identified by quantitative analysis (cluster analysis and correspondence analysis), guided the content qualitative analysis which was carried out addressing three main research questions addressing food shopping routines, feelings of dependency and needs of informal support for shopping, and differences between past and present food shopping behaviours. Living circumstances influence food shopping habits. Informal networks differed between two groups of individuals: those living alone and those living with others. Gender differences emerged in shopping pleasure. Geographical factors were associated with preference for shopping companions, attitudes toward receiving support, and availability of a car for shopping. The importance of living circumstances (i.e., alone vs. with others) in FSW was revealed. Informal social networks may play an important role in public health and welfare policies, particularly given the increase in this demographic group. Assistance with grocery shopping and the availability of trained personnel could widen informal networks, and effective informal networks may be an important supportive service for older adults. The comparison across countries highlighted relationships between food procurement capabilities and social networks. These findings may be used to develop resources to better meet the nutritional needs of older adults.
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