| 1. |
- Berthomier, M., et al.
(författare)
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Alfven : magnetosphere-ionosphere connection explorers
- 2012
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Ingår i: Experimental astronomy. - Dordrecht : Springer. - 0922-6435 .- 1572-9508. ; 33:2-3, s. 445-489
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Tidskriftsartikel (refereegranskat)abstract
- The aurorae are dynamic, luminous displays that grace the night skies of Earth's high latitude regions. The solar wind emanating from the Sun is their ultimate energy source, but the chain of plasma physical processes leading to auroral displays is complex. The special conditions at the interface between the solar wind-driven magnetosphere and the ionospheric environment at the top of Earth's atmosphere play a central role. In this Auroral Acceleration Region (AAR) persistent electric fields directed along the magnetic field accelerate magnetospheric electrons to the high energies needed to excite luminosity when they hit the atmosphere. The "ideal magnetohydrodynamics" description of space plasmas which is useful in much of the magnetosphere cannot be used to understand the AAR. The AAR has been studied by a small number of single spacecraft missions which revealed an environment rich in wave-particle interactions, plasma turbulence, and nonlinear acceleration processes, acting on a variety of spatio-temporal scales. The pioneering 4-spacecraft Cluster magnetospheric research mission is now fortuitously visiting the AAR, but its particle instruments are too slow to allow resolve many of the key plasma physics phenomena. The Alfv,n concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planets.
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| 2. |
- Yao, Shutao, et al.
(författare)
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Observations of kinetic-size magnetic holes in the magnetosheath
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 122:2, s. 1990-2000
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic holes (MHs), with a scale much greater than ρi (proton gyroradius), have been widely reported in various regions of space plasmas. On the other hand, kinetic-size magnetic holes (KSMHs), previously called small-size magnetic holes, with a scale of the order of magnitude of or less than ρi have only been reported in the Earth's magnetospheric plasma sheet. In this study, we report such KSMHs in the magnetosheath whereby we use measurements from the Magnetospheric Multiscale mission, which provides three-dimensional (3-D) particle distribution measurements with a resolution much higher than previous missions. The MHs have been observed in a scale of 10-20 ρe (electron gyroradii) and lasted 0.1-0.3 s. Distinctive electron dynamics features are observed, while no substantial deviations in ion data are seen. It is found that at the 90 degrees pitch angle, the flux of electrons with energy 34-66 eV decreased, while for electrons of energy 109-1024 eV increased inside the MHs. We also find the electron flow vortex perpendicular to the magnetic field, a feature self-consistent with the magnetic depression. Moreover, the calculated current density is mainly contributed by the electron diamagnetic drift, and the electron vortex flow is the diamagnetic drift flow. The electron magnetohydrodynamics soliton is considered as a possible generation mechanism for the KSMHs with the scale size of 10-20 ρe.
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| 3. |
- Yao, S. T., et al.
(författare)
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Propagation of small size magnetic holes in the magnetospheric plasma sheet
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - : Wiley-Blackwell. - 2169-9380 .- 2169-9402. ; 121:6, s. 5510-5519
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic holes (MHs), characteristic structures where the magnetic field magnitude decreases significantly, have been frequently observed in space plasmas. Particularly, small size magnetic holes (SSMHs) which the scale is less than or close to the proton gyroradius are recently detected in the magnetospheric plasma sheet. In this study of Cluster observations, by the timing method, the minimum directional difference (MDD) method, and the spatiotemporal difference (STD) method, we obtain the propagation velocity of SSMHs in the plasma flow frame. Furthermore, based on electron magnetohydrodynamics (EMHD) theory we calculate the velocity, width, and depth of the electron solitary wave and compare it to SSMH observations. The result shows a good accord between the theory and the observation.
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| 4. |
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| 5. |
- Meredith, S. J., et al.
(författare)
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Return to sport after anterior cruciate ligament injury: Panther Symposium ACL Injury Return to Sport Consensus Group
- 2020
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Ingår i: Knee Surgery Sports Traumatology Arthroscopy. - : Springer Science and Business Media LLC. - 0942-2056 .- 1433-7347. ; 28, s. 2403-2414
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Tidskriftsartikel (refereegranskat)abstract
- Purpose A precise and consistent definition of return to sport (RTS) after anterior cruciate ligament (ACL) injury is lacking, and there is controversy surrounding the process of returning patients to sports and their previous activity level. The aim of the Panther Symposium ACL Injury RTS Consensus Group was to provide a clear definition of RTS and description of the RTS continuum, as well as to provide clinical guidance on RTS testing and decision-making. Methods An international, multidisciplinary group of ACL experts convened as part of a consensus meeting. Consensus statements were developed using a modified Delphi method. Literature review was performed to report the supporting evidence. Results Key points include that RTS is characterized by achievement of the pre-injury level of sport and involves a criteria-based progression from return to participation to return to sport, and ultimately return to performance. Purely time-based RTS decision-making should be abandoned. Progression occurs along a RTS continuum with decision-making by a multidisciplinary group that incorporates objective physical examination data and validated and peer-reviewed RTS tests, which should involve functional assessment as well as psychological readiness. Consideration should be given to biological healing, contextual factors and concomitant injuries. Conclusion The resultant consensus statements and scientific rationale aim to inform the reader of the complex process of RTS after ACL injury that occurs along a dynamic continuum. Research is needed to determine the ideal RTS test battery, the best implementation of psychological readiness testing and methods for the biologic assessment of healing and recovery.
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| 6. |
- Meredith, S. J., et al.
(författare)
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Return to sport after anterior cruciate ligament injury: Panther Symposium ACL Injury Return to Sport Consensus Group
- 2021
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Ingår i: Journal of Isakos Joint Disorders & Orthopaedic Sports Medicine. - : Elsevier BV. - 2059-7754. ; 6:3, s. 138-146
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Tidskriftsartikel (refereegranskat)abstract
- Objectives A precise and consistent definition of return to sport (RTS) after anterior cruciate ligament (ACL) injury is lacking, and there is controversy surrounding the process of returning patients to sports and their previous activity level. The aim of the Panther Symposium ACL Injury RTS Consensus Group was to provide a clear definition of RTS after ACL injury and description of the RTS continuum, as well as provide clinical guidance on RTS testing and decision-making. Methods An international, multidisciplinary group of ACL experts convened as part of a consensus meeting. Consensus statements were developed using a modified Delphi method. Literature review was performed to report the supporting evidence. Results Key points include that RTS is characterised by achievement of the preinjury level of sport and involves a criteria-based progression from return to participation to RTS, and ultimately return to performance. Purely time-based RTS decision-making should be abandoned. Progression occurs along an RTS continuum with decision-making by a multidisciplinary group that incorporates objective physical examination data and validated and peer-reviewed RTS tests, which should involve functional assessment as well as psychological readiness. Consideration should be given to biological healing, contextual factors and concomitant injuries. Conclusion The resultant consensus statements and scientific rationale aim to inform the reader of the complex process of RTS after ACL injury that occurs along a dynamic continuum. Research is needed to determine the ideal RTS test battery, the best implementation of psychological readiness testing and methods for the biological assessment of healing and recovery.
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| 7. |
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| 8. |
- Persson, L., et al.
(författare)
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TROPHIC INTERACTIONS IN TEMPERATE LAKE ECOSYSTEMS - A TEST OF FOOD-CHAIN THEORY
- 1992
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Ingår i: American Naturalist. ; 140:1, s. 59-84
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Tidskriftsartikel (refereegranskat)abstract
- In a comparative study covering 11 temperate lake ecosystems of low to intermediate productivity, we tested the predictions of the food chain model developed by L. Oksanen et al. The pelagic habitat of the most unproductive lakes lacked secondary carnivores (piscivores), whereas secondary carnivores inhabited the more productive lakes in agreement with the assumption that food chain length is limited by the productivity of the system. The observed relationships between planktivores (primary carnivores), zooplankton (herbivores), and phytoplankton (primary producers) were in agreement with the predictions of the Oksanen et al. model for three- and four-trophic-link systems. Piscivore relationships were significant only when the biomass of piscivorous perch only was used as the independent variable (piscivorous perch amounted to greater-than-or-equal-to 97% of total piscivore biomass in five out of six four-link systems). The results suggest that gross patterns of food web dynamics in temperate lakes may be collapsed into food chain dynamics. However, as the higher trophic levels of most lakes were dominated by the same two species, an alternative hypothesis is that the simplicity of the food webs studied allowed food chain dynamics to approximate food web dynamics. The food chain model tested gave accurate predictions of trophic-level relationships within the rather narrow productivity range studied. However, previous data suggest that, due to size-structured interactions, secondary carnivores (piscivores) play a minor role in highly productive systems, a circumstance that may explain the postulated increase in mortality rate of zooplankton with increasing productivity. The observed increase in number of trophic levels with productivity does not necessarily imply a causal relationship between productivity and food chain length, as lake productivity is also correlated with structural complexity (in the form of submerged vegetation and an oxygenated hypolimnion). Habitat heterogeneity may thus influence food chain length, and in general it is likely that food chain length will depend on more than one environmental variable.
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| 9. |
- Pitkänen, Timo, 1979-, et al.
(författare)
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IMF By Influence on Magnetospheric Convection in Earth's Magnetotail Plasma Sheet
- 2019
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Ingår i: Geophysical Research Letters. - : Blackwell Publishing Ltd. - 0094-8276 .- 1944-8007. ; 46:21, s. 11698-11708
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Tidskriftsartikel (refereegranskat)abstract
- We use Geotail, Cluster, and Time History of Events and Macroscale Interactions during Substorms data over 15 years (1995–2009) to statistically investigate convective ion flows (V⊥xy<200 km/s) in the magnetotail plasma sheet under the influence of a clearly nonzero dawn-dusk interplanetary magnetic field (IMF By). We find that IMF By causes an interhemispheric asymmetry in the flows, which depends on the direction of IMF By. On the average, one magnetic hemisphere is dominated by a dawn-dusk flow component, which is oppositely directed compared to that in the other hemisphere. This asymmetry is observed for both earthward and tailward flows. A comparison to tail By reveals that the region where the asymmetry in the average flows appears agrees with the appearance of the tail By direction collinear to IMF By. The results imply that IMF By has a major influence on the direction of the magnetic flux transport in the magnetotail.
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| 10. |
- Pitkänen, Timo, 1979-, et al.
(författare)
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Statistical Survey of Magnetic Forces Associated With Earthward Bursty Bulk Flows Measured by MMS 2017-2021
- 2023
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 128:5
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the magnetic forces (the magnetic pressure gradient force, the curvature force, and their sum the j x B-force) associated with earthward bursty bulk flows (BBFs) using Magnetospheric Multiscale (MMS) data from five tail seasons (2017-2021). For the first time, the magnetic forces are inferred downtail of XGSM = -20 R-E and in the GSM XY and YZ planes. The results suggest that BBFs tend to be accelerated earthward by the magnetic pressure gradient force tailward of similar to 19 R-E and decelerated closer to that distance in the 2017-2018 data. The force magnitudes increase with distance. This is in accordance with earlier Cluster results. In the 2019-2021 data, the pressure gradient force magnitudes are generally smaller and no clear distance for the acceleration reversal can be determined. The curvature forces for both 2017-2018 and 2019-2021 BBFs indicate earthward acceleration independent of distance, consistent with the Cluster measurements. The sum, the j x B-force, suggests for the 2017-2018 BBFs earthward acceleration tailward of XGSM similar to 15 R-E and deceleration within that distance, also consistent with Cluster. In contrast, the 2019-2021 BBFs show general earthward acceleration by j x B independent of distance. In the GSM XY plane, the average (j x B)(xy) vectors are earthward, and in the premidnight and postmidnight dawnward for the 2017-2018 BBFs. For 2019-2021, the average (j x B)(xy) vectors have components toward the tail center. In the GSM YZ plane, the average (j x B)(yz) vectors are toward the neutral sheet.
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