| 111. |
- Hansel, P. J., et al.
(författare)
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Mapping MMS Observations of Solitary Waves in Earth's Magnetic Field
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:12
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Tidskriftsartikel (refereegranskat)abstract
- Electrostatic solitary waves (ESWs) are a type of nonlinear time-domain plasma structure (TDS) generally defined by bipolar electric fields and propagation parallel to the local magnetic field. Formation mechanisms for TDSs in the magnetosphere have been studied extensively and are associated with plasma boundary layers and the braking of bursty bulk flows (BBFs). However, the rapid timescales over which these TDSs occur (<2 ms) make them infeasible to count by eye over large time periods. Furthermore, high-cadence data are not always available. The Solitary Wave Detector (SWD) on NASA's Magnetospheric Multiscale (MMS) mission quantifies the occurrence and amplitude of TDS throughout the constellation's orbit; analysis of burst (65 kS/s) parallel electric field data indicates that the SWD captures approximately 60% of all bipolar TDS encountered in the tail region, enabling large-scale examination of their occurrence. Maps of TDS occurrence rates during several years of the MMS mission were generated from SWD data, showing enhanced TDS density in the tail region between 6 and 9 Re; enhance occurrence in or near shocks; and an unexpected enhancement in the dawn side of the tail and in the radiation belt.
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| 112. |
- Kitamura, N., et al.
(författare)
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Observations of the Source Region of Whistler Mode Waves in Magnetosheath Mirror Structures
- 2020
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 125:5
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Tidskriftsartikel (refereegranskat)abstract
- In the magnetosheath, intense whistler mode waves, called "Lion roars," are often detected in troughs of magnetic field intensity in mirror mode structures. Using data obtained by the four Magnetospheric Multiscale (MMS) spacecraft, we show that reversals of gradient of magnetic field intensity along the magnetic field correspond to reversals of the field-aligned component of Poynting flux of whistler mode waves in the troughs. Such a characteristic is consistent with the idea that the whistler mode waves are effectively generated near the local minima of magnetic field intensity because of the smallest cyclotron resonance velocity and propagate toward regions of larger magnetic field intensity along the magnetic field lines on both sides. We use the reversal of the Poynting flux as an indicator of wave source regions. In these regions, we find that pancake or an outer edge of butterfly electron distributions above similar to 100 eV are good candidates for wave generation. Unclear correlations of phase difference and amplitude variations of whistler mode waves in cases of similar to 40 km spacecraft separation indicate that a simple plane wave approximation with a constant amplitude is not valid at this spatial scale that is much smaller than the ion gyroradius. The whistler mode waves consist of small coherent wave packets from multiple sources with spatial scales smaller than tens of electron gyroradii transverse to the background magnetic field in a mirror mode structure.
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| 113. |
- Makos, I., et al.
(författare)
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Attosecond photoelectron spectroscopy using high-harmonic generation and seeded free-electron lasers
- 2023
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Ingår i: 2023 Photonics North, PN 2023. - 9798350326734
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Konferensbidrag (refereegranskat)abstract
- In this work, we use attosecond time-resolved techniques to investigate photoionization dynamics on its natural timescale, employing both high harmonic generation and seeded free-electron lasers to generate extreme ultraviolet attosecond pulse trains for our studies. With the former approach, we examine the role of nuclear motion in molecular photoionization dynamics, while with the latter we introduce a novel attosecond timing tool for single-shot characterization of the relative phase between the XUV and the infrared field.
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| 114. |
- Oieroset, M., et al.
(författare)
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Spatial evolution of magnetic reconnection diffusion region structures with distance from the X-line
- 2021
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 28:12
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Tidskriftsartikel (refereegranskat)abstract
- We report Magnetospheric Multiscale four-spacecraft observations of a thin reconnecting current sheet with weakly asymmetric inflow conditions and a guide field of approximately twice the reconnecting magnetic field. The event was observed at the interface of interlinked magnetic field lines at the flank magnetopause when the maximum spacecraft separation was 370 km and the spacecraft covered & SIM;1.7 ion inertial lengths (d(i)) in the reconnection outflow direction. The ion-scale spacecraft separation made it possible to observe the transition from electron-only super ion-Alfvenic outflow near the electron diffusion region (EDR) to the emergence of sub-Alfvenic ion outflow in the ion diffusion region (IDR). The EDR to IDR evolution over a distance less than 2 d(i) also shows the transition from a near-linear reconnecting magnetic field reversal to a more bifurcated current sheet as well as significant decreases in the parallel electric field and dissipation. Both the ion and electron heating in this diffusion region event were similar to the previously reported heating in the far downstream exhausts. The dimensionless reconnection rate, obtained four different ways, was in the range of 0.13-0.27. This event reveals the rapid spatial evolution of the plasma and electromagnetic fields through the EDR to IDR transition region.& nbsp;(C) 2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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| 115. |
- Sangchooli, Arshiya, et al.
(författare)
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Parameter Space and Potential for Biomarker Development in 25 Years of fMRI Drug Cue Reactivity
- 2024
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Ingår i: JAMA psychiatry. - : AMER MEDICAL ASSOC. - 2168-6238 .- 2168-622X.
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Forskningsöversikt (refereegranskat)abstract
- Importance In the last 25 years, functional magnetic resonance imaging drug cue reactivity (FDCR) studies have characterized some core aspects in the neurobiology of drug addiction. However, no FDCR-derived biomarkers have been approved for treatment development or clinical adoption. Traversing this translational gap requires a systematic assessment of the FDCR literature evidence, its heterogeneity, and an evaluation of possible clinical uses of FDCR-derived biomarkers. Objective To summarize the state of the field of FDCR, assess their potential for biomarker development, and outline a clear process for biomarker qualification to guide future research and validation efforts. Evidence Review The PubMed and Medline databases were searched for every original FDCR investigation published from database inception until December 2022. Collected data covered study design, participant characteristics, FDCR task design, and whether each study provided evidence that might potentially help develop susceptibility, diagnostic, response, prognostic, predictive, or severity biomarkers for 1 or more addictive disorders. Findings There were 415 FDCR studies published between 1998 and 2022. Most focused on nicotine (122 [29.6%]), alcohol (120 [29.2%]), or cocaine (46 [11.1%]), and most used visual cues (354 [85.3%]). Together, these studies recruited 19 311 participants, including 13 812 individuals with past or current substance use disorders. Most studies could potentially support biomarker development, including diagnostic (143 [32.7%]), treatment response (141 [32.3%]), severity (84 [19.2%]), prognostic (30 [6.9%]), predictive (25 [5.7%]), monitoring (12 [2.7%]), and susceptibility (2 [0.5%]) biomarkers. A total of 155 interventional studies used FDCR, mostly to investigate pharmacological (67 [43.2%]) or cognitive/behavioral (51 [32.9%]) interventions; 141 studies used FDCR as a response measure, of which 125 (88.7%) reported significant interventional FDCR alterations; and 25 studies used FDCR as an intervention outcome predictor, with 24 (96%) finding significant associations between FDCR markers and treatment outcomes. Conclusions and Relevance Based on this systematic review and the proposed biomarker development framework, there is a pathway for the development and regulatory qualification of FDCR-based biomarkers of addiction and recovery. Further validation could support the use of FDCR-derived measures, potentially accelerating treatment development and improving diagnostic, prognostic, and predictive clinical judgments.
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| 116. |
- Stawarz, J. E., et al.
(författare)
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Comparative Analysis of the Various Generalized Ohm's Law Terms in Magnetosheath Turbulence as Observed by Magnetospheric Multiscale
- 2021
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 126:1
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Tidskriftsartikel (refereegranskat)abstract
- Decomposing the electric field (E) into the contributions from generalized Ohm's law provides key insight into both nonlinear and dissipative dynamics across the full range of scales within a plasma. Using high-resolution, multispacecraft measurements of three intervals in Earth's magnetosheath from the Magnetospheric Multiscale mission, the influence of the magnetohydrodynamic, Hall, electron pressure, and electron inertia terms from Ohm's law, as well as the impact of a finite electron mass, on the turbulent E spectrum are examined observationally for the first time. The magnetohydrodynamic, Hall, and electron pressure terms are the dominant contributions to E over the accessible length scales, which extend to scales smaller than the electron gyroradius at the greatest extent, with the Hall and electron pressure terms dominating at sub-ion scales. The strength of the nonideal electron pressure contribution is stronger than expected from linear kinetic Alfven waves and a partial antialignment with the Hall electric field is present, linked to the relative importance of electron diamagnetic currents in the turbulence. The relative contribution of linear and nonlinear electric fields scale with the turbulent fluctuation amplitude, with nonlinear contributions playing the dominant role in shaping E for the intervals examined in this study. Overall, the sum of the Ohm's law terms and measured E agree to within similar to 20% across the observable scales. These results both confirm general expectations about the behavior of E in turbulent plasmas and highlight features that should be explored further theoretically.
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| 117. |
- Wilder, F. D., et al.
(författare)
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Multipoint Measurements of the Electron Jet of Symmetric Magnetic Reconnection with a Moderate Guide Field
- 2017
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 118:26
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Tidskriftsartikel (refereegranskat)abstract
- We report observations from the Magnetospheric Multiscale (MMS) satellites of the electron jet in a symmetric magnetic reconnection event with moderate guide field. All four spacecraft sampled the ion diffusion region and observed the electron exhaust. The observations suggest that the presence of the guide field leads to an asymmetric Hall field, which results in an electron jet skewed towards the separatrix with a nonzero component along the magnetic field. The jet appears in conjunction with a spatially and temporally persistent parallel electric field ranging from -3 to -5 mV/m, which led to dissipation on the order of 8 nW/m(3). The parallel electric field heats electrons that drift through it, and is associated with a streaming instability and electron phase space holes.
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| 118. |
- Wilder, F. D., et al.
(författare)
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The Role of the Parallel Electric Field in Electron-Scale Dissipation at Reconnecting Currents in the Magnetosheath
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 123:8, s. 6533-6547
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Tidskriftsartikel (refereegranskat)abstract
- We report observations from the Magnetospheric Multiscale satellites of reconnecting current sheets in the magnetosheath over a range of out-of-plane "guide" magnetic field strengths. The currents exhibit nonideal energy conversion in the electron frame of reference, and the events are within the ion diffusion region within close proximity (a few electron skin depths) to the electron diffusion region. The study focuses on energy conversion on the electron scale only. At low guide field (antiparallel reconnection), electric fields and currents perpendicular to the magnetic field dominate the energy conversion. Additionally, electron distributions exhibit significant nongyrotropy. As the guide field increases, the electric field parallel to the background magnetic field becomes increasingly strong, and the electron nongyrotropy becomes less apparent. We find that even with a guide field less than half the reconnecting field, the parallel electric field and currents dominate the dissipation. This suggests that parallel electric fields are more important to energy conversion in reconnection than previously thought and that at high guide field, the physics governing magnetic reconnection are significantly different from antiparallel reconnection.
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| 119. |
- Ertel, D., et al.
(författare)
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Ultrastable, high-repetition-rate attosecond beamline for time-resolved XUV-IR coincidence spectroscopy
- 2023
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Ingår i: Review of Scientific Instruments. - 0034-6748. ; 94:7
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Tidskriftsartikel (refereegranskat)abstract
- The implementation of attosecond photoelectron-photoion coincidence spectroscopy for the investigation of atomic and molecular dynamics calls for a high-repetition-rate driving source combined with experimental setups characterized by excellent stability for data acquisition over time intervals ranging from a few hours up to a few days. This requirement is crucial for the investigation of processes characterized by low cross sections and for the characterization of fully differential photoelectron(s) and photoion(s) angular and energy distributions. We demonstrate that the implementation of industrial-grade lasers, combined with a careful design of the delay line implemented in the pump-probe setup, allows one to reach ultrastable experimental conditions leading to an error in the estimation of the time delays of only 12 as over an acquisition time of 6.5 h. This result opens up new possibilities for the investigation of attosecond dynamics in simple quantum systems.
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| 120. |
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