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  • 1
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    Understanding the variability of nightside temperatures, NO UV and O2 IR nightglow emissions in the Venus upper atmosphere (2011)
    Wiley
    Details
    Publication Date: 2011-08-16
    Description: Venus Express (VEX) has been monitoring key nightglow emissions and thermal features (O2 IR nightglow, NO UV nightglow, and nightside temperatures) which contribute to a comprehensive understanding of the global dynamics and circulation patterns above ∼90 km. The nightglow emissions serve as effective tracers of Venus' middle and upper atmosphere global wind system due to their variable peak brightness and horizontal distributions. A statistical map has been created utilizing O2 IR nightglow VEX observations, and a statistical map for NO UV is being developed. A nightside warm layer near 100 km has been observed by VEX and ground-based observations. The National Center for Atmospheric Research (NCAR) Venus Thermospheric General Circulation Model (VTGCM) has been updated and revised in order to address these key VEX observations and to provide diagnostic interpretation. The VTGCM is first used to capture the statistically averaged mean state of these three key observations. This correspondence implies a weak retrograde superrotating zonal flow (RSZ) from ∼80 km to 110 km and above 110 km the emergence of modest RSZ winds approaching 60 m s−1 above ∼130 km. Subsequently, VTGCM sensitivity tests are performed using two tuneable parameters (the nightside eddy diffusion coefficient and the wave drag term) to examine corresponding variability within the VTGCM. These tests identified a possible mechanism for the observed noncorrelation of the O2 and NO emissions. The dynamical explanation requires the nightglow layers to be at least ∼15 km apart and the retrograde zonal wind to increase dramatically over 110 to 130 km.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Electronic Resource
    Electronic Resource
    The High-Temperature Transformation of MoGe2 (1959)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 63 (1959), S. 2058-2059 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j150582a020
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    Paper (German National Licenses)
    Fulltext
  • 3
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    The multiple spots of the Ganymede auroral footprint (2013)
    Wiley
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    Publication Date: 2013-10-01
    Description: [1]  The interaction between the moons and the magnetosphere of giant planets sometimes gives rise to auroral signatures in the planetary ionosphere, called the satellite footprints. So far, footprints have been detected for Io, Europa, Ganymede and Enceladus. These footprints are usually seen as single spots. However, the Io footprint, the brightest one, displays a much more complex morphology made of at least three different spots and an extended tail. Here, we present Hubble Space Telescope FUV images showing evidence for a second spot in the Ganymede footprint. The spots separation distance changes as Ganymede moves latitudinally in the plasma sheet, as is seen for the Io footprint. This indicates that the processes identified at Io are universal. Moreover, for similar Ganymede System III longitudes, the distance may also vary significantly with time, indicating changes in the plasma sheet density. We identified a rapid evolution of this distance ~8 days after the detection of a volcanic outburst at Io, suggesting that such auroral observations could be used to estimate the plasma density variations at Ganymede.
    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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  • 4
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    Influence of dimensionality and interface type on optical and electronic properties of CdS/ZnS core-shell nanocrystals—A first-principles study (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-10-23
    Description: Semiconducting nanocrystals (NCs) have become one of the leading materials in a variety of applications, mainly due to their size tunable band gap and high intensity emission. Their photoluminescence (PL) properties can be notably improved by capping the nanocrystals with a shell of another semiconductor, making core-shell structures. We focus our study on the CdS/ZnS core-shell nanocrystals that are closely related to extensively studied CdSe/CdS NCs, albeit exhibiting rather different photoluminescence properties. We employ density functional theory to investigate the changes in the electronic and optical properties of these nanocrystals with size, core/shell ratio, and interface structure between the core and the shell. We have found that both the lowest unoccupied eigenstate (LUES) and the highest occupied eigenstate (HOES) wavefunction (WF) are localized in the core of the NCs, with the distribution of the LUES WF being more sensitive to the size and the core/shell ratio. We show that the radiative lifetimes are increasing, and the Coulomb interaction energies decrease with increasing NC size. Furthermore, we investigated the electronic and optical properties of the NCs with different interfaces between the core and the shell and different core types. We find that the different interfaces and core types have rather small influence on the band gaps and the absorption indexes, as well as on the confinement of the HOES and LUES WFs. Also the radiative lifetimes are found to be only slightly influenced by the different structural models. In addition, we compare these results with the previous results for CdSe/CdS NCs, reflecting the different PL properties of these two types of NCs. We argue that the difference in their Coulomb interaction energies is one of the main reasons for their distinct PL properties.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    SNP-markers in Allium species to facilitate introgression breeding in onion (2016)
    BioMed Central
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    Publication Date: 2016-09-01
    Description: Within onion, Allium cepa L., the availability of disease resistance is limited. The identification of sources of resistance in related species, such as Allium roylei and Allium fistulosum, was a first step towar...
    Electronic ISSN: 1471-2229
    Topics: Biology
    Published by BioMed Central
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  • 6
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    Concurrent observations of ultraviolet aurora and energetic electron precipitation with Mars Express (2015)
    Wiley
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    Publication Date: 2015-07-02
    Description: The database of the Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument between late January 2004 and Mars 2014 has been searched to identify signatures of CO Cameron and CO 2 + doublet ultraviolet auroral emissions. This study has almost doubled the number of auroral detections based on SPICAM spectra. Auroral emissions are located in the vicinity of the statistical boundary between open and closed field lines. From a total of 113 nightside orbits with SPICAM pointing to the nadir in the region of residual magnetic field, only nine show confirmed auroral signatures, some with multiple detections along the orbital track, leading to a total of 16 detections. The mean energy of the electron energy spectra measured during concurrent ASPERA-3/ELS observations ranges from 150 to 280 eV. The ultraviolet aurora may be displaced poleward or equatorward of the region of enhanced downward electron energy flux by several tens of seconds and shows no proportionality with the electron flux at the spacecraft altitude. The absence of further UV auroral detection in regions located along crustal magnetic field structures where occasional aurora has been observed indicates that the Mars aurora is a time dependent feature. These results are consistent with the scenario of acceleration of electrons by transient parallel electric field along semi open magnetic field lines.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Bifurcations of the main auroral ring at Saturn: ionospheric signatures of consecutive reconnection events at the magnetopause (2011)
    Wiley
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    Publication Date: 2011-11-10
    Description: This work reports for the first time on bifurcations of the main auroral ring at Saturn observed with the UVIS instrument onboard Cassini. The observation sequence starts with an intensification on the main oval, close to noon, which is possibly associated with dayside reconnection. Consecutive bifurcations appear with the onset of dayside reconnection, between 11 and 18 magnetic local time, while the area poleward of the main emission expands to lower latitudes. The bifurcations depart with time from the main ring of emission, which is related to the open-closed field line boundary. The augmentation of the area poleward of the main emission following its expansion is balanced by the area occupied by the bifurcations, suggesting that these auroral features represent the amount of newly open flux and could be related to consecutive reconnection events at the flank of the magnetopause. The observations show that the open flux along the sequence increases when bifurcations appear. Magnetopause reconnection can lead to significant augmentation of the open flux within a couple of days and each reconnection event opens ∼10% of the flux contained within the polar cap. Additionally, the observations imply an overall length of the reconnection line of ∼4 hours of local time and suggest that dayside reconnection at Saturn can occur at several positions on the magnetopause consecutively or simultaneously.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    He2+ transport in the Martian upper atmosphere with an induced magnetic field (2013)
    Wiley
    Details
    Publication Date: 2013-02-16
    Description: [1]  Solar wind helium may be a significant source of neutral helium in the Martian atmosphere. The precipitating particles also transfer mass, energy and momentum. To investigate the transport of He 2+ in the upper atmosphere of Mars we have applied the Direct Simulation Monte Carlo method to solve the kinetic equation. We calculate the upward He, He + and He 2+ fluxes, resulting from energy spectra of the downgoing He 2+ observed below 500 km altitude by the ASPERA-3 instrument onboard Mars Express. The particle flux of the downward moving He 2+ ions was 1-2 × 10 6  cm -2  s -1 , and the energy flux is equal to 9-10 × 10 -3 erg cm -2  s -1 . The calculations of the upward flux have been made for the Martian atmosphere during solar minimum. [2]  It was found, that if the induced magnetic field is not introduced in the simulations the precipitating He 2+ ions are not backscattered at all by the Martian upper atmosphere. If we include a 20 nT horizontal magnetic field, a typical field measured by Mars Global Surveyor (MGS) in the altitude range of 85 km – 500 km, we find that up to the 30% - 40% of the energy flux of the precipitating He 2+ ions is backscattered depending on the velocity distribution of the precipitating particles. We thus conclude that the induced magnetic field plays the crucial role in the transport of charged particles in the upper atmosphere of Mars and, therefore, that it determines the energy deposition of the solar wind.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 9
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    Signatures of magnetospheric injections in Saturn's aurora (2013)
    Wiley
    Details
    Publication Date: 2013-02-05
    Description: [1]  We report on the evolution of auroral structures based on two 3-hour sequences of Saturn's northern hemisphere obtained with the UVIS instrument on board Cassini and we discuss their possible association with injections in the magnetosphere of Saturn.Simultaneously with the UV auroral structures we observe Energetic Neutral Atom (ENA) enhancements which are indicative of a rotating heated plasma region possibly related to magnetospheric injections. We examine the possibility that the UV auroral structures reported here are triggered by energetic particle injections by investigating a) the evolution of the longitudinal extent of an injection and b) its energy density, properties that change with time due to dispersion and ion/electron losses. We simulate the auroral counterpart of an injection considering that the precipitating energy flux could be provided to the ionosphere by pitch angle diffusion and electron scattering by whistler-mode waves. We compare the brightness and size evolution ofthe simulated ionospheric signature with the observed values and we demonstrate that the UV auroral structure behaves as an auroral signature of an injection. This comparative study defines characteristics of the injections such as the spectral index and the electron energy range as well as the magnetospheric corotation rate. Additionally, based on the simultaneous ENA-UV emissions we discuss the possibility that pitch angle diffusion and electron scattering may not be the only mechanism responsible for the observed auroral emissions. Field aligned currents driven by the pressure gradients along the boundaries of the injected hot plasma cloud could be also considered to play a role on how injections create auroral emissions at Saturn.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    Auroral spirals at Saturn (2015)
    Wiley
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    Publication Date: 2015-09-29
    Description: We report observations of auroral spirals at Saturn propagating from midnight to noon via dawn, based on Cassini/UVIS measurements. The aurora during that sequence is observed for the first time to consist of detached features swirling as they propagate from dawn to early afternoon. The features have a diameter of ∼6000 km in the ionosphere, which would correspond to 12 to 15 R S -wide plasma regions in the magnetosphere. Simultaneous ENA enhancements are observed, however, they do not show a clear spiral form. We estimate the velocity of the UV auroral features to decrease from 85% of rigid corotation (28°/h) near the equatorward edge to 68% of rigid corotation (22°/h) in the poleward edge. We discuss two posible scenarios which could explain the generation of the auroral spirals. Firstly, we suggest that the auroral spirals could be related to large dynamic hot populations which create regions with strong velocity gradients. Alternatively, a less possible theory could be that the auroral spirals are related to field line deformation from the magnetosphere to the ionosphere, similar to the scenario proposed to explain auroral spirals at Earth. Such field line twist can happen for a configuration where the magnetospheric source region is located between a pair of plasma flow vortices.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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