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  • 1
    Online Resource
    Online Resource
    Evaluation of scaffold microstructure and comparison of cell seeding methods using micro-computed tomography-based tools
    The Royal Society ; 2020
    In:  Journal of The Royal Society Interface Vol. 17, No. 165 ( 2020-04), p. 20200102-
    Details
    In: Journal of The Royal Society Interface, The Royal Society, Vol. 17, No. 165 ( 2020-04), p. 20200102-
    Abstract: Micro-computed tomography (micro-CT) provides a means to analyse and model three-dimensional (3D) tissue engineering scaffolds. This study proposes a set of micro-CT-based tools firstly for evaluating the microstructure of scaffolds and secondly for comparing different cell seeding methods. The pore size, porosity and pore interconnectivity of supercritical CO 2 processed poly( l -lactide-co- ɛ -caprolactone) (PLCL) and PLCL/β-tricalcium phosphate scaffolds were analysed using computational micro-CT models. The models were supplemented with an experimental method, where iron-labelled microspheres were seeded into the scaffolds and micro-CT imaged to assess their infiltration into the scaffolds. After examining the scaffold architecture, human adipose-derived stem cells (hASCs) were seeded into the scaffolds using five different cell seeding methods. Cell viability, number and 3D distribution were evaluated. The distribution of the cells was analysed using micro-CT by labelling the hASCs with ultrasmall paramagnetic iron oxide nanoparticles. Among the tested seeding methods, a forced fluid flow-based technique resulted in an enhanced cell infiltration throughout the scaffolds compared with static seeding. The current study provides an excellent set of tools for the development of scaffolds and for the design of 3D cell culture experiments.
    Type of Medium: Online Resource
    ISSN: 1742-5689 , 1742-5662
    URL: Article
    DOI: 10.1098/rsif.2020.0102
    Language: English
    Publisher: The Royal Society
    Publication Date: 2020
    detail.hit.zdb_id: 2156283-0
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  • 2
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    Particle telescope aboard FORESAIL-1: Simulated performance
    Elsevier BV ; 2020
    In:  Advances in Space Research Vol. 66, No. 1 ( 2020-07), p. 29-41
    Details
    In: Advances in Space Research, Elsevier BV, Vol. 66, No. 1 ( 2020-07), p. 29-41
    Type of Medium: Online Resource
    ISSN: 0273-1177
    URL: Article
    DOI: 10.1016/j.asr.2019.11.010
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2020
    detail.hit.zdb_id: 2023311-5
    SSG: 16,12
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  • 3
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    The impact on global magnetohydrodynamic simulations from varying initialisation methods: results from GUMICS-4
    Copernicus GmbH ; 2017
    In:  Annales Geophysicae Vol. 35, No. 4 ( 2017-08-01), p. 907-922
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 35, No. 4 ( 2017-08-01), p. 907-922
    Abstract: Abstract. We investigate the effects of different initialisation methods of the GUMICS-4 global magnetohydrodynamic (MHD) simulation to the dynamics in different parts of the Earth's magnetosphere and hence compare five 12 h simulation runs that were initiated by 3 h of synthetic data and followed by 9 h of solar wind measurements using the OMNI data as input. As a reference, we use a simulation run that includes nearly 60 h of OMNI data as input prior to the 9 h interval examined with different initialisations. The selected interval is a high-speed stream event during a 10-day interval (12–22 June 2007). The synthetic initialisations include stepwise, linear and sinusoidal functions of the interplanetary magnetic field with constant density and velocity values. The results show that the solutions converge within 1 h to give a good agreement in both the bow shock and the magnetopause position. However, the different initialisation methods lead to local differences which should be taken into consideration when comparing model results to satellite measurements.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-35-907-2017
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2017
    detail.hit.zdb_id: 1458425-6
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  • 4
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    Tail reconnection in the global magnetospheric context: Vlasiator first results
    Copernicus GmbH ; 2017
    In:  Annales Geophysicae Vol. 35, No. 6 ( 2017-11-28), p. 1269-1274
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 35, No. 6 ( 2017-11-28), p. 1269-1274
    Abstract: Abstract. The key dynamics of the magnetotail have been researched for decades and have been associated with either three-dimensional (3-D) plasma instabilities and/or magnetic reconnection. We apply a global hybrid-Vlasov code, Vlasiator, to simulate reconnection self-consistently in the ion kinetic scales in the noon–midnight meridional plane, including both dayside and nightside reconnection regions within the same simulation box. Our simulation represents a numerical experiment, which turns off the 3-D instabilities but models ion-scale reconnection physically accurately in 2-D. We demonstrate that many known tail dynamics are present in the simulation without a full description of 3-D instabilities or without the detailed description of the electrons. While multiple reconnection sites can coexist in the plasma sheet, one reconnection point can start a global reconfiguration process, in which magnetic field lines become detached and a plasmoid is released. As the simulation run features temporally steady solar wind input, this global reconfiguration is not associated with sudden changes in the solar wind. Further, we show that lobe density variations originating from dayside reconnection may play an important role in stabilising tail reconnection.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    URL: Article
    DOI: 10.5194/angeo-35-1269-2017
    DOI: 10.5194/angeo-35-1269-2017-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2017
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  • 5
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    Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions
    Copernicus GmbH ; 2019
    In:  Annales Geophysicae Vol. 37, No. 5 ( 2019-09-10), p. 791-806
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 37, No. 5 ( 2019-09-10), p. 791-806
    Abstract: Abstract. Particle precipitation plays a key role in the coupling of the terrestrial magnetosphere and ionosphere by modifying the upper atmospheric conductivity and chemistry, driving field-aligned currents, and producing aurora. Yet quantitative observations of precipitating fluxes are limited, since ground-based instruments can only provide indirect measurements of precipitation, while particle telescopes aboard spacecraft merely enable point-like in situ observations with an inherently coarse time resolution above a given location. Further, orbit timescales generally prevent the analysis of whole events. On the other hand, global magnetospheric simulations can provide estimations of particle precipitation with a global view and higher time resolution. We present the first results of auroral (∼1–30 keV) proton precipitation estimation using the Vlasiator global hybrid-Vlasov model in a noon–midnight meridional plane simulation driven by steady solar wind with a southward interplanetary magnetic field. We first calculate the bounce loss-cone angle value at selected locations in the simulated nightside magnetosphere. Then, using the velocity distribution function representation of the proton population at those selected points, we study the population inside the loss cone. This enables the estimation of differential precipitating number fluxes as would be measured by a particle detector aboard a low-Earth-orbiting (LEO) spacecraft. The obtained differential flux values are in agreement with a well-established empirical model in the midnight sector, as are the integral energy flux and mean precipitating energy. We discuss the time evolution of the precipitation parameters derived in this manner in the global context of nightside magnetospheric activity in this simulation, and we find in particular that precipitation bursts of 〈1 min duration can be self-consistently and unambiguously associated with dipolarising flux bundles generated by tail reconnection. We also find that the transition region seems to partly regulate the transmission of precipitating protons to the inner magnetosphere, suggesting that it has an active role in regulating ionospheric precipitation.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    URL: Article
    DOI: 10.5194/angeo-37-791-2019
    DOI: 10.5194/angeo-37-791-2019-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 1458425-6
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  • 6
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    Evidence for transient, local ion foreshocks caused by dayside magnetopause reconnection
    Copernicus GmbH ; 2016
    In:  Annales Geophysicae Vol. 34, No. 11 ( 2016-11-04), p. 943-959
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 34, No. 11 ( 2016-11-04), p. 943-959
    Abstract: Abstract. We present a scenario resulting in time-dependent behaviour of the bow shock and transient, local ion reflection under unchanging solar wind conditions. Dayside magnetopause reconnection produces flux transfer events driving fast-mode wave fronts in the magnetosheath. These fronts push out the bow shock surface due to their increased downstream pressure. The resulting bow shock deformations lead to a configuration favourable to localized ion reflection and thus the formation of transient, travelling foreshock-like field-aligned ion beams. This is identified in two-dimensional global magnetospheric hybrid-Vlasov simulations of the Earth's magnetosphere performed using the Vlasiator model (http://vlasiator.fmi.fi). We also present observational data showing the occurrence of dayside reconnection and flux transfer events at the same time as Geotail observations of transient foreshock-like field-aligned ion beams. The spacecraft is located well upstream of the foreshock edge and the bow shock, during a steady southward interplanetary magnetic field and in the absence of any solar wind or interplanetary magnetic field perturbations. This indicates the formation of such localized ion foreshocks.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    URL: Article
    DOI: 10.5194/angeo-34-943-2016
    DOI: 10.5194/angeo-34-943-2016-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2016
    detail.hit.zdb_id: 1458425-6
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  • 7
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    Magnetosheath jet properties and evolution as determined by a global hybrid-Vlasov simulation
    Copernicus GmbH ; 2018
    In:  Annales Geophysicae Vol. 36, No. 5 ( 2018-09-07), p. 1171-1182
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 36, No. 5 ( 2018-09-07), p. 1171-1182
    Abstract: 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 ∼0.5 RE. 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.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    URL: Article
    DOI: 10.5194/angeo-36-1171-2018
    DOI: 10.5194/angeo-36-1171-2018-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2018
    detail.hit.zdb_id: 1458425-6
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  • 8
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    Helium in the Earth's foreshock: a global Vlasiator survey
    Copernicus GmbH ; 2020
    In:  Annales Geophysicae Vol. 38, No. 5 ( 2020-10-20), p. 1081-1099
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 38, No. 5 ( 2020-10-20), p. 1081-1099
    Abstract: Abstract. The foreshock is a region of space upstream of the Earth's bow shock extending along the interplanetary magnetic field (IMF). It is permeated by shock-reflected ions and electrons, low-frequency waves, and various plasma transients. We investigate the extent of the He2+ foreshock using Vlasiator, a global hybrid-Vlasov simulation. We perform the first numerical global survey of the helium foreshock and interpret some historical foreshock observations in a global context. The foreshock edge is populated by both proton and helium field-aligned beams, with the proton foreshock extending slightly further into the solar wind than the helium foreshock and both extending well beyond the ultra-low frequency (ULF) wave foreshock. We compare our simulation results with Magnetosphere Multiscale (MMS) Hot Plasma Composition Analyzer (HPCA) measurements, showing how the gradient of suprathermal ion densities at the foreshock crossing can vary between events. Our analysis suggests that the IMF cone angle and the associated shock obliquity gradient can play a role in explaining this differing behaviour. We also investigate wave–ion interactions with wavelet analysis and show that the dynamics and heating of He2+ must result from proton-driven ULF waves. Enhancements in ion agyrotropy are found in relation to, for example, the ion foreshock boundary, the ULF foreshock boundary, and specular reflection of ions at the bow shock. We show that specular reflection can describe many of the foreshock ion velocity distribution function (VDF) enhancements. Wave–wave interactions deep in the foreshock cause de-coherence of wavefronts, allowing He2+ to be scattered less than protons.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-38-1081-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 1458425-6
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  • 9
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    Foreshock cavitons and spontaneous hot flow anomalies: a statistical study with a global hybrid-Vlasov simulation
    Copernicus GmbH ; 2021
    In:  Annales Geophysicae Vol. 39, No. 5 ( 2021-10-14), p. 911-928
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 39, No. 5 ( 2021-10-14), p. 911-928
    Abstract: Abstract. The foreshock located upstream of Earth's bow shock hosts a wide variety of phenomena related to the reflection of solar wind particles from the bow shock and the subsequent formation of ultra-low-frequency (ULF) waves. In this work, we investigate foreshock cavitons, which are transient structures resulting from the non-linear evolution of ULF waves, and spontaneous hot flow anomalies (SHFAs), which are thought to evolve from cavitons as they accumulate suprathermal ions while being carried to the bow shock by the solar wind. Using the global hybrid-Vlasov simulation model Vlasiator, we have conducted a statistical study in which we track the motion of individual cavitons and SHFAs in order to examine their properties and evolution. In our simulation run where the interplanetary magnetic field (IMF) is directed at a sunward–southward angle of 45∘, continuous formation of cavitons is found up to ∼11 Earth radii (RE) from the bow shock (along the IMF direction), and caviton-to-SHFA evolution takes place within ∼2 RE from the shock. A third of the cavitons in our run evolve into SHFAs, and we find a comparable amount of SHFAs forming independently near the bow shock. We compare the properties of cavitons and SHFAs to prior spacecraft observations and simulations, finding good agreement. We also investigate the variation of the properties as a function of position in the foreshock, showing that transients close to the bow shock are associated with larger depletions in the plasma density and magnetic field magnitude, along with larger increases in the plasma temperature and the level of bulk flow deflection. Our measurements of the propagation velocities of cavitons and SHFAs agree with earlier studies, showing that the transients propagate sunward in the solar wind rest frame. We show that SHFAs have a greater solar wind rest frame propagation speed than cavitons, which is related to an increase in the magnetosonic speed near the bow shock.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-39-911-2021
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2021
    detail.hit.zdb_id: 1458425-6
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  • 10
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    Flux-tube-dependent propagation of Alfvén waves in the solar corona
    EDP Sciences ; 2022
    In:  Astronomy & Astrophysics Vol. 661 ( 2022-05), p. A58-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 661 ( 2022-05), p. A58-
    Abstract: Context. Alfvén-wave turbulence has emerged as an important heating mechanism to accelerate the solar wind. The generation of this turbulent heating is dependent on the presence and subsequent interaction of counter-propagating Alfvén waves. This requires us to understand the propagation and evolution of Alfvén waves in the solar wind in order to develop an understanding of the relationship between turbulent heating and solar-wind parameters. Aims. We aim to study the response of the solar wind upon injecting monochromatic single-frequency Alfvén waves at the base of the corona for various magnetic flux-tube geometries. Methods. We used an ideal magnetohydrodynamic model using an adiabatic equation of state. An Alfvén pump wave was injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components. Results. Alfvén waves were found to be reflected due to the development of the parametric decay instability (PDI). Further investigation revealed that the PDI was suppressed both by efficient reflections at low frequencies as well as magnetic flux-tube geometries.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/202142999
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2022
    detail.hit.zdb_id: 1458466-9
    SSG: 16,12
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