| 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. |
- Biasi, P., et al.
(författare)
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Revealing the role of bromide in the H2O2 direct synthesis with the catalyst wet pretreatment method (CWPM)
- 2017
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Ingår i: AIChE Journal. - : American Institute of Chemical Engineers. - 0001-1541 .- 1547-5905. ; 63:1, s. 32-42
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Tidskriftsartikel (refereegranskat)abstract
- A tailor-made Pd0/K2621 catalyst was subjected to post synthesis modification via a wet treatment procedure. The aimwas the understanding of the role of promoters and how—if any—improvements could be qualitatively related to the cat-alyst performance for the H2O2direct synthesis. The Catalyst Wet Pretreatment Method was applied in different metha-nolic solutions containing H2O2, NaBr, and H3PO4, either as single modifiers or as a mixture. The catalyst wascharacterized by Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy. It was concluded that themodified catalysts give rise to higher selectivities compared to the pristi ne reference catalyst thus opening a possibilityto exclude the addit ion of the undesirable selectivity enhancers in the reaction medium. This work provides original evi-dence on the role of promoter s, especially bromide, allowing the formulation of a new reaction mechanism for one ofthe most challenging reactions recognized by the world.
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| 3. |
- Décréau, P.M.E. , Fergeau, P., Krasnosels'kikh, V., Le Guirriec, E., Lévêque , M., Martin, Ph. , Randriamboarison, O., Rauch, J. L., Sené, F. X., Séran, H. C., Trotignon, J.G. , Canu, P., Cornilleau, N., de Féraudy, H., Alleyne, H. , Yearby, K., Mögensen
(författare)
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Early results from the Whisper instrument on Cluster: an overview.
- 2001
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Ingår i: Annales Geophysicae. ; 19:10, s. . 1241-1258
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Tidskriftsartikel (refereegranskat)abstract
- The Whisper instrument yields two data sets: (i) the electron density determined via the relaxation sounder, and (ii) the spectrum of natural plasma emissions in the frequency band 2-80 kHz. Both data sets allow for the three-dimensional exploration of th
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| 4. |
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| 5. |
- Bernardini, A., et al.
(författare)
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Direct synthesis of H2O2 over Pd supported on rare earths promoted zirconia
- 2015
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 256, s. 294-301
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Tidskriftsartikel (refereegranskat)abstract
- In this work Pd (0.3 or 0.6 wt.%) was supported on both ZrxM1-xO2 (M = La, Y, Ce) and on mechanical mixtures of CeO2 and ZrO2. The synthesized catalysts were characterized by XRD, TPR, AAS and CO chemisorption and tested for the direct synthesis of hydrogen peroxide in a high pressure semibatch apparatus. The reactants conversion was limited in order to avoid mass-transfer limitations. No selectivity enhancers of any kind were used and the all the materials were halide free. Small metal particles were obtained (1-2.6 nm). Supports with smaller pore diameters leaded to larger Pd particles, which in turn were found to preferentially support the formation of the peroxide. Moreover, supports with higher reducibility favored the production of H2O2, probably due to an easier reduction of the active metal, essential to achieve high selectivity. Notwithstanding the absence of enhancers, the specific activity and selectivity recorded were very high.
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| 6. |
- Cherenko, M., et al.
(författare)
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Venous thromboembolism in Cushing syndrome: results from an EuRRECa and Endo-ERN survey
- 2024
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Ingår i: Endocrine Connections. - 2049-3614. ; 13:6
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Tidskriftsartikel (refereegranskat)abstract
- Background: Patients with Cushing syndrome (CS) are at increased risk of venous thromboembolism (VTE). Objective: The aim was to evaluate the current management of new cases of CS with a focus on VTE and thromboprophylaxis. Design and methods: A survey was conducted within those that report in the electronic reporting tool (e-REC) of the European Registries for Rare Endocrine Conditions (EuRRECa) and the involved main thematic groups (MTG’s) of the European Reference Networks for Rare Endocrine Disorders (Endo-ERN) on new patients with CS from January 2021 to July 2022. Results: Of 222 patients (mean age 44 years, 165 females), 141 patients had Cushing disease (64%), 69 adrenal CS (31%), and 12 patients with ectopic CS (5.4%). The mean follow-up period post-CS diagnosis was 15 months (range 3–30). Cortisol-lowering medications were initiated in 38% of patients. One hundred fifty-four patients (69%) received thromboprophylaxis (including patients on chronic anticoagulant treatment), of which low-molecular-weight heparins were used in 96% of cases. VTE was reported in six patients (2.7%), of which one was fatal: two long before CS diagnosis, two between diagnosis and surgery, and two postoperatively. Three patients were using thromboprophylaxis at time of the VTE diagnosis. The incidence rate of VTE in patients after Cushing syndrome diagnosis in our study cohort was 14.6 (95% CI 5.5; 38.6) per 1000 person-years. Conclusion: Thirty percent of patients with CS did not receive preoperative thromboprophylaxis during their active disease stage, and half of the VTE cases even occurred during this stage despite thromboprophylaxis. Prospective trials to establish the optimal thromboprophylaxis strategy in CS patients are highly needed. Significance statement The incidence rate of venous thromboembolism in our study cohort was 14.6 (95% CI 5.5; 38.6) per 1000 person-years. Notably, this survey showed that there is great heterogeneity regarding time of initiation and duration of thromboprophylaxis in expert centers throughout Europe.
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| 7. |
- Garnier, P., et al.
(författare)
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Titan's ionosphere in the magnetosheath : Cassini RPWS results during the T32 flyby
- 2009
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:11, s. 4257-4272
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Tidskriftsartikel (refereegranskat)abstract
- The Cassini mission has provided much information about the Titan environment, with numerous low altitude encounters with the moon being always inside the magnetosphere. The only encounter taking place outside the magnetopause, in the magnetosheath, occurred the 13 June 2007 (T32 flyby). This paper is dedicated to the analysis of the Radio and Plasma Wave investigation data during this specific encounter, in particular with the Langmuir probe, providing a detailed picture of the cold plasma environment and of Titan's ionosphere with these unique plasma conditions. The various pressure terms were also calculated during the flyby. The comparison with the T30 flyby, whose geometry was very similar to the T32 encounter but where Titan was immersed in the kronian magnetosphere, reveals that the evolution of the incident plasma has a significant influence on the structure of the ionosphere, with in particular a change of the exo-ionospheric shape. The electrical conductivities are given along the trajectory of the spacecraft and the discovery of a polar plasma cavity is reported.
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| 8. |
- Horbury, T., et al.
(författare)
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Cross-scale : A multi-spacecraft mission to study cross-scale coupling in space plasmas
- 2006
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Ingår i: European Space Agency, (Special Publication) ESA SP. ; , s. 561-568
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Konferensbidrag (refereegranskat)abstract
- Collisionless astrophysical plasmas exhibit complexity on many scales: if we are to understand their properties and effects, we must measure this complexity. We can identify a small number of processes and phenomena, one of which is dominant in almost every space plasma region of interest: shocks, reconnection and turbulence. These processes act to transfer energy between locations, scales and modes. However, this transfer is characterised by variability and 3D structure on at least three scales: electron kinetic, ion kinetic and fluid. It is the nonlinear interaction between physical processes at these scales that is the key to understanding these phenomena and predicting their effects. However, current and planned multi-spacecraft missions such as Cluster and MMS only study variations on one scale in 3D at any given time - we must measure the three scales simultaneously fully to understand the energy transfer processes. We propose a mission, called Cross-Scale, to study these processes. Cross-Scale would comprise three nested groups, each consisting of up to four spacecraft. Each group would have a different spacecraft separation, at approximately the electron and ion gyroradii, and a larger MHD scale. We would therefore be able to measure variations on all three important physical scales, simultaneously, for the first time. The spacecraft would fly in formation through key regions of near-Earth space: The solar wind, bowshock, magnetosheath, magnetopause and magnetotail.
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| 9. |
- Kurth, W.S., Hospodarsky, G.B., Gurnett, D.A., Kaiser, M.L., Wahlund, J.E., Roux, A., Canu, P., Zarka, P. and Tokarev, Y.
(författare)
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An overview of observations by the Cassini radio and plasma wave investigation at Earth.
- 2001
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Ingår i: Journal of Geophysical Research. ; 106:A12, s. 30239-
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Tidskriftsartikel (refereegranskat)abstract
- On August 18, 1999, the Cassini spacecraft flew by Earth at an altitude of 1186 km on its way to Saturn. Although the flyby was performed exclusively to provide the spacecraft with sufficient velocity to get to Saturn, the radio and plasma wave science (R
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| 10. |
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| 11. |
- Modolo, Ronan, et al.
(författare)
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Plasma environment in the wake of Titan from hybrid simulation : A case study
- 2007
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 34:24, s. L24S07-
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Tidskriftsartikel (refereegranskat)abstract
- On 26 December 2005, the Cassini spacecraft flew through Titan's plasma wake and revealed a complex and dynamic region. Observations suggest a strong asymmetry which seems to be displaced from the ideal position of the wake. Two distinct plasma regions are identified with a significant difference on the electron number density and on the plasma composition. Simulation results using a three-dimensional and multi-species hybrid model, performed in conditions similar to those encountered during the flyby, are presented and compared to the observations. An acceptable agreement is shown between the model predictions and the observations. We suggest that the observed asymmetries, in terms of density and plasma composition, are mainly caused by the a combination of the asymmetry in the ion/electron production rate and the magnetic field morphology, where the first plasma region is connected to the dayside hemisphere of Titan's ionosphere while the other is connected to the nightside hemisphere.
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| 12. |
- Alqeeq, S. W., et al.
(författare)
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Investigation of the homogeneity of energy conversion processes at dipolarization fronts from MMS measurements
- 2022
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Ingår i: Physics of Plasmas. - : American Institute of Physics (AIP). - 1070-664X .- 1089-7674. ; 29:1
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Tidskriftsartikel (refereegranskat)abstract
- We report on six dipolarization fronts (DFs) embedded in fast earthward flows detected by the Magnetospheric Multiscale mission during a substorm event on 23 July 2017. We analyzed Ohm's law for each event and found that ions are mostly decoupled from the magnetic field by Hall fields. However, the electron pressure gradient term is also contributing to the ion decoupling and likely responsible for an electron decoupling at DF. We also analyzed the energy conversion process and found that the energy in the spacecraft frame is transferred from the electromagnetic field to the plasma (J & BULL; E > 0) ahead or at the DF, whereas it is the opposite (J & BULL; E < 0) behind the front. This reversal is mainly due to a local reversal of the cross-tail current indicating a substructure of the DF. In the fluid frame, we found that the energy is mostly transferred from the plasma to the electromagnetic field (J & BULL; E & PRIME; < 0) and should contribute to the deceleration of the fast flow. However, we show that the energy conversion process is not homogeneous at the electron scales due to electric field fluctuations likely related to lower-hybrid drift waves. Our results suggest that the role of DF in the global energy cycle of the magnetosphere still deserves more investigation. In particular, statistical studies on DF are required to be carried out with caution due to these electron scale substructures.
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| 13. |
- Alqeeq, S. W., et al.
(författare)
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Two Classes of Equatorial Magnetotail Dipolarization Fronts Observed by Magnetospheric Multiscale Mission : A Statistical Overview
- 2023
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 128:10
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Tidskriftsartikel (refereegranskat)abstract
- We carried out a statistical study of equatorial dipolarization fronts (DFs) detected by the Magnetospheric Multiscale mission during the full 2017 Earth's magnetotail season. We found that two DF classes are distinguished: class I (74.4%) corresponds to the standard DF properties and energy dissipation and a new class II (25.6%). This new class includes the six DF discussed in Alqeeq et al. (2022, ) and corresponds to a bump of the magnetic field associated with a minimum in the ion and electron pressures and a reversal of the energy conversion process. The possible origin of this second class is discussed. Both DF classes show that the energy conversion process in the spacecraft frame is driven by the diamagnetic current dominated by the ion pressure gradient. In the fluid frame, it is driven by the electron pressure gradient. In addition, we have shown that the energy conversion processes are not homogeneous at the electron scale mostly due to the variations of the electric fields for both DF classes.
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| 14. |
- Chasapis, A., et al.
(författare)
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Thin Current Sheets and Associated Electron Heating in Turbulent Space Plasma
- 2015
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing (IOPP). - 2041-8205 .- 2041-8213. ; 804:1
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Tidskriftsartikel (refereegranskat)abstract
- Intermittent structures, such as thin current sheets, are abundant in turbulent plasmas. Numerical simulations indicate that such current sheets are important sites of energy dissipation and particle heating occurring at kinetic scales. However, direct evidence of dissipation and associated heating within current sheets is scarce. Here, we show a new statistical study of local electron heating within proton-scale current sheets by using high-resolution spacecraft data. Current sheets are detected using the Partial Variance of Increments (PVI) method which identifies regions of strong intermittency. We find that strong electron heating occurs in high PVI (>3) current sheets while no significant heating occurs in low PVI cases (<3), indicating that the former are dominant for energy dissipation. Current sheets corresponding to very high PVI (>5) show the strongest heating and most of the time are consistent with ongoing magnetic reconnection. This suggests that reconnection is important for electron heating and dissipation at kinetic scales in turbulent plasmas.
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| 15. |
- Farrell, W. M., et al.
(författare)
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Mass unloading along the inner edge of the Enceladus plasma torus
- 2008
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 35:2, s. L02203-
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Tidskriftsartikel (refereegranskat)abstract
- A major discovery made by the Cassini spacecraft at Saturn was the substantial mass ejection from the south pole of Enceladus. Previous studies show that this ejected gas can become ionized and subsequently load mass onto the connecting magnetic field lines near the moon. Radial diffusion then allows the mass-loaded field lines to move outward to similar to 15 R-s and inward to similar to 2 R-s, forming a plasma torus. We demonstrate herein that the mass is also '' unloaded '' along the inner edge of this plasma torus the edge incident with the plasma-absorbing A-ring. Interpreting down-drifting z-mode tones from active sites along the inner edge of the ion torus as emission near the local electron plasma frequency, f(pe), we can remotely-monitor this reduction in plasma density along the torus inner edge as a function time. We find that the down-drift of the z-mode tones corresponds typically to a plasma density change dn/dt similar to - 5x10(-4)/cm(3)-s and when integrated over an annulus defined by the outer edge of the A-ring, corresponds to a mass loss of similar to 40 kg/s. Using the z-mode tones, we also find locations where plasma mass from the ring-ionosphere is possibly loaded at 1 - 2 kg/s onto field lines near the Cassini gap.
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| 16. |
- Hasegawa, H., et al.
(författare)
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Kelvin-Helmholtz waves at the Earth's magnetopause : Multiscale development and associated reconnection
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 114:12, s. A12207-
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Tidskriftsartikel (refereegranskat)abstract
- We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at similar to 1500 magnetic local time (MLT) by the Geotail spacecraft and at similar to 1900 MLT by the Cluster spacecraft, which detected rolled-up MHD-scale vortices generated by the Kelvin-Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD-scale and ion-scale structures of the vortices, and the formation mechanism of the low-latitude boundary layer (LLBL). The observed KH wavelength (>4 x 10(4) km) is considerably longer than predicted by the linear theory from the thickness (similar to 1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high-latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length similar to 100 km and of magnetic shear similar to 60 degrees existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvenic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field-aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk-flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster.
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| 17. |
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| 18. |
- Lanza, Roberto, et al.
(författare)
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Methane partial oxidation over Pt-Ru catalyst : An investigation on the mechanism
- 2010
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 375:1, s. 92-100
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Tidskriftsartikel (refereegranskat)abstract
- The mechanism of the partial oxidation of methane has been investigated over a bimetallic Pt-Ru catalyst. Dedicated experiments aimed to separate and quantify the relative contribution of single reactions included in the so-called "combustion and reforming" mechanism using the same catalyst. The catalyst is 0.5% Ru and 0.5% Pt (w/w) supported on mixture of alumina, ceria and zirconia (75/4.4/20.6%, w/w), washcoated on a ceramic monolith. Steam reforming, dry reforming, direct and reverse water-gas shift reactions were investigated. The temperature range investigated is 300 < T < 800 degrees C, while the space velocity range is 25.000 < GHSV < 100.000 h(-1). Conditions at which single side reactions are expected to occur during the partial oxidation process, were approximated by tuning the reactant composition. The experimental results are also compared with thermodynamic equilibrium calculations. The CO and H-2 yields of partial oxidation have been quantitatively connected with steam and dry reforming, while the persistent water-gas shift reaction always rearranges the products and intermediates.
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| 19. |
- Lanza, Roberto, et al.
(författare)
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Microemulsion-prepared ruthenium catalyst for syngas production via methane partial oxidation
- 2008
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 337:1, s. 10-18
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Tidskriftsartikel (refereegranskat)abstract
- Partial oxidation of methane (POxM) was studied over Ru catalyst supported on alumina (1%, w/w). The catalyst was prepared via microemulsion (ME) and coated onto cordierite monoliths. Samples were characterized by XRD, BET surface area, SEM-EDS and TPR and TPO analyses. The catalyst showed high methane conversion with very good selectivity towards CO and H-2 under every condition tested. The effects of GHSV and heating rate (HR) were investigated, recording composition data both during heating and cooling. This allowed to evidence hysteresis cycles and to obtain additional information on the reactions occurring within the monolith.
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| 20. |
- Lanza, Roberto, et al.
(författare)
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Partial oxidation of methane over Pt-Ru bimetallic catalyst for syngas production
- 2008
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 348:2, s. 221-228
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Tidskriftsartikel (refereegranskat)abstract
- A bimetallic catalyst (Pt-Ru 50/50) has been prepared for methane partial oxidation. Total metal load was 1 wt%. The support was alumina mixed with 25 wt% of a ceria-zirconia mixture. This because of the good performances of alumina for such applications and to exploit the oxygen buffer effect of the ceriazirconia system. The catalyst has been prepared by incipient wetness and characterized by means of XRD, BET surface area, TPR/TPO and SEM-EDS analyses. It showed good activity and high selectivity towards CO and H-2, produced in a ratio suitable for Fisher-Tropsch applications. The effect of spatial velocity (GHSV) has been investigated; ramping temperature up and down, some hysteresis has been evidenced, especially at the highest GHSV, mainly caused by thermal effects. Overall, 100% conversion of methane to H-2 and CO at the appropriate syngas ratio (2/1) can achieved easily and with stability.
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| 21. |
- Lanza, Roberto, et al.
(författare)
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Partial oxidation of methane over supported ruthenium catalysts
- 2007
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 325:1, s. 57-67
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Tidskriftsartikel (refereegranskat)abstract
- Partial oxidation of methane (POM) to synthesis gas was studied over Ru catalysts (1% (w/w)) supported on silica, alumina and ceria-zirconia. Catalyst samples were prepared by incipient wetness and characterized by BET area, XRD, ESEM-EDS, and TPR-TPO analyses. Ru on silica deactivated very fast, while Ru supported on alumina has good activity and selectivity. The mixture CeO2-ZrO2 led to low selectivity towards POM, with a higher selectivity towards complete combustion, common to all the catalysts at lower temperature. Both reduced and non-reduced catalysts were tested resulting in different behaviour in the same temperature range. We investigated the effect of different GHSVs, heating rates and also sequences of heating and cooling cycles. This allowed gaining insight into the sequence of reactions taking place in the reactor and revealed hysteresis for all reaction conditions. This can be explained through a cycling between Ru oxidation states on the surface.
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| 22. |
- Modolo, Ronan, et al.
(författare)
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Far plasma wake of Titan from the RPWS observations : A case study
- 2007
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 34:24, s. L24S04-
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Tidskriftsartikel (refereegranskat)abstract
- The Titan's plasma wake has been investigated using observations from the Radio and Plasma Wave Science (RPWS) instrument onboard the Cassini spacecraft during one Titan flyby on December 26, 2005. The Langmuir Probe and the wideband receiver suggest a strong asymmetry of the plasma wake, which is displaced from the ideal wake. Two distinct structures are identified inbound and outbound of the flyby with significantly different electron number densities (ne). The maximum electron number density reached 14 cm(-3) on the Saturn side, connected to the sunlit ionosphere, while on the opposite side of Saturn observations indicate a density smaller than 2 cm(-3). Other derived parameters of the Langmuir probe analysis suggest also a difference in plasma composition between the two structures, where heavy and light ions dominate the Saturn and anti- Saturn side respectively. The total ion outflow is estimated at 2-7 x 10(25) ions/s assuming a cylindrical geometry for the plasma wake.
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| 23. |
- Roberts, O. W., et al.
(författare)
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Scale-Dependent Kurtosis of Magnetic Field Fluctuations in the Solar Wind : A Multi-Scale Study With Cluster 2003-2015
- 2022
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 127:9
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Tidskriftsartikel (refereegranskat)abstract
- During the lifetime of the Cluster mission, the inter-spacecraft distances in the solar wind have changed from the large, fluid, scales (similar to 10(4) km), down to the scales of protons (similar to 10(2) km). As part of the guest investigator campaign, the mission achieved a formation where a pair of spacecraft were separated by similar to 7 km. The small distances and the exceptional sensitivity of the search coil magnetometer provide an excellent data set for studying solar wind turbulence at electron scales. In this study, we investigate the intermittency of the magnetic field fluctuations in the slow solar wind. Using 20 time intervals with different constellation orientations of Cluster we cover spatial scales between 7 and 10(4) km. We compare time-lagged increments from a single spacecraft with spatially lagged increments using multiple spacecraft. As the turbulent cascade proceeds to smaller scales in the inertial range, the deviation from Gaussian statistics is observed to increase in both temporal and spatial increments in the components transverse to the mean field direction. At ion scales, there is a maximum of kurtosis, and at sub-ion scales, the fluctuations are only weakly non-Gaussian. In the compressive component the deviation from Gaussian statistics is variable: it may increase throughout the inertial and sub-ion ranges, but also, it may have a maximum at magnetohydrodynamic scales associated with large scale magnetic holes. The observations show differences in kurtosis of time and space increments when the spacecraft pairs are transverse to the flow, indicating its spatial anisotropy. Plain Language Summary Turbulence in the slow solar wind is investigated using multi-spacecraft measurements for different satellites configurations. Twenty time intervals of more than 1 hr are analyzed. We compare differences in two time-delayed magnetic field measurements (time-lags) and of magnetic field measurements between spacecraft pairs (space-lags). Space-lags give the fluctuations along different satellite baseline directions and scales (from 7 to 9,000 km) while time-lags give the fluctuations along the flow direction. The magnetic field fluctuations' intermittency, which can be thought of as the "patchiness" or "roughness" is investigated. Differences are observed between the time-lagged measurements and the spatially lagged measurements when the spacecraft pairs are transverse to the flow.
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| 24. |
- Romanelli, N., et al.
(författare)
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Outflow and plasma acceleration in Titan's induced magnetotail : Evidence of magnetic tension forces
- 2014
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 119:12
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Tidskriftsartikel (refereegranskat)abstract
- Cassini plasma wave and particle observations are combined with magnetometer measurements to study Titan's induced magnetic tail. In this study, we report and analyze the plasma acceleration in Titan's induced magnetotail observed in flybys T17, T19, and T40. Radio and Plasma Wave Science observations show regions of cold plasma with electron densities between 0.1 and a few tens of electrons per cubic centimeter. The Cassini Plasma Spectrometer (CAPS)-ion mass spectrometer (IMS) measurements suggest that ionospheric plasma in this region is composed of ions with masses ranging from 15 to 17 amu and from 28 to 31 amu. From these measurements, we determine the bulk velocity of the plasma and the Alfven velocity in Titan's tail region. Finally, a Walen test of such measurements suggest that the progressive acceleration of the ionospheric plasma shown by CAPS can be interpreted in terms of magnetic tension forces.
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| 25. |
- Scarabello, Andrea, et al.
(författare)
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Partial oxidation of methane on Rh/ZrO2 and Rh/Ce-ZrO2 on monoliths : Catalyst restructuring at reaction conditions
- 2015
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 174-175, s. 308-322
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Tidskriftsartikel (refereegranskat)abstract
- 0.5% Rh catalysts on ZrO2 or CeO2-ZrO2, coated on monoliths were tested for partial oxidation of methane, (GHSV=100000h-1). We ran temperature cycles up to 850°C, varying the O2/CH4 ratio from 0.5 to 0.7. The catalysts were characterized by XRD, TPR/TPO, BET and chemisorption. ZrO2 required a long conditioning step, to reach stable performance, while the CeO2-ZrO2 catalyst quickly gained steady activity. The conditioning step is explained with a restructuring of the surface, with the metallic particles becoming smaller. Ceria lowers the ignition temperature by 60°C. At low temperature, ceria allows an increase in CH4 conversion and selectivity to syngas. At high temperature, the CeO2-ZrO2 catalyst significantly increases the CH4 conversion, compared to ZrO2, approaching 100%. However, the selectivity to syngas decreases below 80%. The syngas selectivity is higher at lower O2/CH4 ratio, at any temperature, but the absolute amount of syngas can be larger with more O2.
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