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  • 1
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    Preparation, Properties, and Reactivity of (Aminoferrocenyl)(ferrocenyl)carbene(pentacarbonyl)chromium(0) as Bulky Isolobal Trimetallo-amide (2015)
    Wiley
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    Publication Date: 2015-08-12
    Description: Nucleophilic substitution of the ethoxy substituent in the Fischer carbene complex (ethoxy)(ferrocenyl)carbene(pentacarbonyl)chromium(0) ( 1 ) by ferrocenyl amide [Fc-NH] – [2 - H] – gives the hetero trimetallic complex (aminoferrocenyl)(ferrocenyl)carbene (pentacarbonyl)chromium(0) ( 3 ). As the Cr(CO) 5 fragment is isolobal to oxygen or sulfur 3 can be viewed as an isolobal metallo analogue to diferrocenylamide (Fc)(FcNH)C=O ( 4 ) and diferrocenylthioamide (Fc)(FcNH)C=S ( 5 ). The impact of the formal replacement of O/S by Cr(CO) 5 in 3 is studied with respect to steric and electronic consequences as well as reactivity by spectroscopic, diffraction, electrochemical and theoretical methods.
    Print ISSN: 0044-2313
    Electronic ISSN: 1521-3749
    Topics: Chemistry and Pharmacology
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  • 2
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    Ionospheric response to the 2015 St. Patrick's Day storm: A global multi-instrumental overview (2015)
    Wiley
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    Publication Date: 2015-09-26
    Description: We present the first multi-instrumental results on the ionospheric response to the geomagnetic storm of 17-18 March 2015 (the St. Patrick's Day storm) that was up to now the strongest in the 24 th solar cycle (minimum SYM-H value of -233 nT). The storm caused complex effects around the globe. The most dramatic positive ionospheric storm occurred at low-latitudes in the morning (~100-150% enhancement) and post-sunset (~80-100% enhancement) local sectors. These significant vertical total electron content (VTEC) increases were observed in different local time (LT) sectors and at different universal time (UT), but around the same area of the Eastern Pacific region, which indicates a regional impact of storm drivers. Our analysis revealed that this particular region was most concerned by the increase in the thermospheric O/N2 ratio. At mid-latitudes, we observe inverse hemispheric asymmetries that occurred, despite the equinoctial period, in different longitudinal regions. In the European-African sector, positive storm signatures were observed in the Northern Hemisphere (NH), whereas in the American sector, a large positive storm occurred in the Southern Hemisphere (SH), while the NH experienced a negative storm. The observed asymmetries can be partly explained by the thermospheric composition changes and partly by the hemispherically different non-dipolar portions of the geomagnetic field as well as by the IMF By component variations. At high-latitudes, negative ionospheric storm effects were recorded in all longitudinal regions, especially the NH of the Asian sector was concerned. The negative storm phase developed globally on March 18 at the beginning of the recovery phase.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Upper atmosphere differences between northern and southern high-latitudes: the role of magnetic field asymmetry (2013)
    Wiley
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    Publication Date: 2013-09-13
    Description: [1]  The non-dipolar portions of the Earth's main magnetic field constitute substantial differences between the two hemispheres. Beside the magnetic flux densities and patterns being different in the Northern Hemisphere (NH) and Southern Hemisphere (SH), also the offset between the invariant magnetic and the geographic poles is larger in the SH than in the NH. We investigated the effects of this magnetic field asymmetry on the high-latitude thermosphere and ionosphere using global numerical simulations, and compared our results with recent observations. While the effects on the high-latitude plasma convection are small, the consequences for the neutral wind circulation are substantial. The cross-polar neutral wind and ion drift velocities are generally larger in the NH than the SH, and the hemispheric difference shows a semidiurnal variation. The neutral wind vorticity is likewise larger in the NH than in the SH, with the difference probably becoming larger for higher solar activity. In contrast, the spatial variance of the neutral wind is considerably larger in the SH polar region, with the hemispheric difference showing a strong semidiurnal variation. Its phase is similar to the phase of the semidiurnal variation of the hemispheric magnitude differences. Hemispheric differences in ion drift and neutral wind magnitude are most likely caused partly by the larger magnetic flux densities in the near-polar regions of the SH, and partly by the larger offset between the invariant and geographic pole in the SH, while differences in spatial variance are probably just caused by the latter. We conclude that the asymmetry of the magnetic field, both in strength and in orientation, establishes substantial hemispheric differences in the neutral wind and plasma drift in the high-latitude upper atmosphere, which can help to explain observed hemispheric differences with EDI/Cluster and CHAMP.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 4
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    Interhemispheric differences in ionospheric convection: Cluster EDI observations revisited (2015)
    Wiley
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    Publication Date: 2015-05-09
    Description: The interaction between the interplanetary magnetic field and the geomagnetic field sets up a large scale circulation in the magnetosphere. This circulation is also reflected in the magnetically connected ionosphere. In this paper, we present a study of ionospheric convection based on Cluster EDI satellite measurements covering both hemispheres, and obtained over a full solar cycle. The results from this study show that average flow patterns and polar cap potentials for a given orientation of the interplanetary magnetic field can be very different in the two hemispheres. In particular during southward directed interplanetary magnetic field conditions, and thus enhanced energy input from the solar wind, the measurements show that the southern polar cap has a higher cross polar cap potential. There are persistent north–south asymmetries, which cannot easily be explained by the influence of external drivers. These persistent asymmetries are primarily a result of the significant differences in the strength and configuration of the geomagnetic field between the Northern and Southern Hemisphere. Since the ionosphere is magnetically connected to the magnetosphere, this difference will also be reflected in the magnetosphere in the form of different feedback from the two hemispheres. Consequently, local ionospheric conditions and the geomagnetic field configuration are important for north–south asymmetries in large regions of geospace.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 5
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    North-South asymmetries in the polar thermosphere-ionosphere system: Solar cycle and seasonal influences (2015)
    Wiley
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    Publication Date: 2015-12-13
    Description: Previous studies have revealed that ion drift and neutral wind speeds at ~400 km in the polar cap (〉80° magnetic latitude) are on average larger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH), which is at least partly due to asymmetry in the geomagnetic field. Here we investigate for the first time how these asymmetries depend on season and on solar/geomagnetic activity levels. Ion drift measurements from the Cluster mission show little seasonal dependence in their North-South asymmetry when all data (Feb 2001-Dec 2013) are used, but the asymmetry disappears around June solstice for high solar activity and around December solstice for low solar activity. Neutral wind speeds in the polar cap obtained from the Challenging Minisatellite Payload (CHAMP) spacecraft (Jan 2002-Dec 2008) are always larger in the summer hemisphere, regardless of solar activity, but the high-latitude neutral wind vortices at dawn and dusk tend to be stronger in the NH, except around December solstice, in particular when solar activity is low. Simulations with the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) more or less capture the behaviour of the ion drift speeds, which can be explained as a superposition of seasonal and geomagnetic field effects, with the former being stronger for higher solar activity. The behaviour of the neutral wind speed and vorticity is not accurately captured by the model. This is probably due to an incorrect seasonal cycle in plasma density around ~400 km in CMIT, which affects the ion drag force. This must be addressed in future work.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 6
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    High emissions of greenhouse gases from grasslands on peat and other organic soils (2016)
    Wiley
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    Publication Date: 2016-04-01
    Description: Drainage has turned peatlands from a carbon sink into one of the world's largest greenhouse gas (GHG) sources from cultivated soils. We analyzed a unique data set (12 peatlands, 48 sites and 122 annual budgets) of mainly unpublished GHG emissions from grasslands on bog and fen peat as well as other soils rich in soil organic carbon (SOC) in Germany. Emissions and environmental variables were measured with identical methods. Site-averaged GHG budgets were surprisingly variable (29.2 ± 17.4 t CO 2 -eq. ha −1 yr −1 ) and partially higher than all published data and the IPCC default emission factors for GHG inventories. Generally, CO 2 (27.7 ± 17.3 t CO 2 ha −1 yr −1 ) dominated the GHG budget. Nitrous oxide (2.3 ± 2.4 kg N 2 O-N ha −1 yr −1 ) and methane emissions (30.8 ± 69.8 kg CH 4 -C ha −1 yr −1 ) were lower than expected except for CH 4 emissions from nutrient-poor acidic sites. At single peatlands, CO 2 emissions clearly increased with deeper mean water table depth (WTD), but there was no general dependency of CO 2 on WTD for the complete data set. Thus, regionalisation of CO 2 emissions by WTD only will remain uncertain. WTD dynamics explained some of the differences between peatlands as sites which became very dry during summer showed lower emissions. We introduced the aerated nitrogen stock (N air ) as a variable combining soil nitrogen stocks with WTD. CO 2 increased with N air across peatlands. Soils with comparatively low SOC concentrations showed as high CO 2 emissions as true peat soils because N air was similar. N 2 O emissions were controlled by the WTD dynamics and the nitrogen content of the topsoil. CH 4 emissions can be well described by WTD and ponding duration during summer. Our results can help both to improve GHG emission reporting and to prioritize and plan emission reduction measures for peat and similar soils at different scales. This article is protected by copyright. All rights reserved.
    Print ISSN: 1354-1013
    Electronic ISSN: 1365-2486
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
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  • 7
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    Late Pleistocene Eifel eruptions: insights from clinopyroxene and glass geochemistry of tephra layers from Eifel Laminated Sediment Archive sediment cores (2019)
    Wiley
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    Publication Date: 2019
    Description: ABSTRACT The Eifel Laminated Sediment Archive (ELSA), which comprises several cores from maar lakes, includes numerous tephra layers spanning the last 140 000 years. The sediment cores are dated by 14C and thermoluminescence as well as tuned to Greenland stadial–interstadial successions. Within the last glacial cycle, the Eifel Volcanic Fields are source to several widespread tephra layers, namely the Laacher See, Eltville, Rambach and Rocourt Tephra. However, a corresponding source volcano was so far only identified for the Laacher See Tephra. In this study we use glass and clinopyroxene geochemistry to link the remaining tephra layers to possible eruption centers within the West and East Eifel Volcanic Fields: while we demonstrate that the Eltville Tephra originated from an earlier eruption of the Laacher See Volcano at 24 300 a bp from within the East Eifel Volcanic Field, the Rambach and Rocourt Tephras are sourced from the West Eifel Volcanic Field and erupted from Wartgesberg at 27 900 a bp and Pulvermaar at 75 000 a bp, respectively. Phases of volcanic activity peaked at 10 000–30 000 and 60 000–80 000 a bp and were thus erupted around the temperature minima of the last glacial cycle. The longest phase of dormancy between individual vents was around 30 000 years long, within the last interglacial.
    Print ISSN: 0267-8179
    Electronic ISSN: 1099-1417
    Topics: Geography , Geosciences
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  • 8
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    The Crystal Structure of the THF Adduct of Monolithioferrocene (2015)
    Wiley
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    Publication Date: 2015-01-21
    Description: Single crystals of [Fe(η 5 -C 5 H 4 )(η 5 -C 5 H 5 )] 2 Li 2 (thf) 4 ( 1 ) were obtained from a tetrahydrofuran solution containing monolithioferrocene. The title compound crystallizes in the monoclinic space group P 2 1 with a = 9.6589(5) Å, b = 17.4285(9) Å, c = 30.3116(15) Å, β = 91.911(2)° and V = 5099.8(5) Å 3 with three independent molecules of 1 . All individual molecules feature a non- symmetric almost planar Li 2 C 2 four-membered ring with two shorter (2.118–2.215 Å) and two longer Li–C distances (2.257–2.309 Å). The lithium cations are each coordinated by two carbanionic atoms of two ferrocenyl substituents and two tetrahydrofuran molecules in a distorted tetrahedral fashion. All ferrocenyl moieties display an eclipsed conformation of the C 5 rings.
    Print ISSN: 0044-2313
    Electronic ISSN: 1521-3749
    Topics: Chemistry and Pharmacology
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  • 9
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    Estimating the capture and loss of cold plasma from ionospheric outflow (2012)
    Wiley
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    Publication Date: 2012-07-18
    Description: An important source of magnetospheric plasma is cold plasma from the terrestrial ionosphere. Low energy ions travel along the magnetic field lines and enter the magnetospheric lobes where they are convected toward the tail plasma sheet. Recent observations indicate that the field aligned ion outflow velocity is sometimes much higher than the convection toward the central plasma sheet. A substantial amount of plasma therefore escapes downtail without ever reaching the central plasma sheet. In this work, we use Cluster measurements of cold plasma outflow and lobe convection velocities combined with models of the magnetic field in an attempt to determine the fate of the outflowing ions and to quantify the amount of plasma lost downtail. The results show that both the circulation of plasma and the direct tailward escape of ions varies significantly with magnetospheric conditions. For strong solar wind driving with a southward interplanetary magnetic field, also typically associated with high geomagnetic activity, most of the outflowing plasma is convected to the plasma sheet and recirculated. For periods with northward interplanetary magnetic field, the convection is nearly stagnant, whereas the outflow, although limited, still persists. The dominant part of the outflowing ions escape downtail and are directly lost into the solar wind under such conditions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
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    F2-region atmospheric gravity waves due to high-power HF heating and subauroral polarization streams (2012)
    Wiley
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    Publication Date: 2012-06-01
    Description: We report the first evidence of atmospheric gravity waves (AGWs) generated in the F2 region by high-power HF heating and subauroral polarization streams. Data come from the CHAMP and GRACE spacecraft overflying the High-frequency Active Auroral Research Program (HAARP) heating facility. These observations facilitate a new method of studying the ionosphere-thermosphere coupling in a controlled fashion by using various HF-heating regimes. They also reveal the subauroral F2 region to be a significant source of substorm AGWs, in addition to the well-known auroral E region.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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