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  • 1
    Publikationsdatum: 2015-05-09
    Beschreibung: Dipolarization fronts (DFs) are believed to play important roles in transferring plasmas, magnetic fluxes and energies in the magnetotail. Using the Cluster observations in 2003, electromagnetic energy conversion at the DFs is investigated by case and statistical studies. The case study indicates strongest energy conversion at the DF. The statistical study shows the similar features that the energy of the fields can be significantly transferred to the plasmas (load, J·E 〉0) at the DFs. These results are consistent with some recent simulations. Examining the electromagnetic fluctuations at the DFs, we suggest that the wave activities around the lower hybrid frequency may play an important role in the energy dissipation.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2016-07-05
    Beschreibung: Whistler waves are believed to play an important role during magnetic reconnection. Here we report the near-simultaneous occurrence of two types of the whistler-mode waves in the magnetotail Hall reconnection region. The first type is observed in the magnetic pileup region of downstream and propagates away to downstream along the field lines, and is possibly generated by the electron temperature anisotropy at the magnetic equator. The second type, propagating towards the X-line, is found around the separatrix region and probably is generated by the electron beam-driven whistler instability or Čerenkov emission from electron phase-space holes. These observations of two different types of whistler waves are consistent with recent kinetic simulations, and suggest that the observed whistler waves are a consequence of magnetic reconnection.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2016-06-15
    Beschreibung: Substorms are fundamental and dynamic processes in the magnetosphere, converting captured solar wind magnetic energy into plasma energy. These substorms have been suggested to be a key driver of energetic electron enhancements in the outer radiation belts. Substorms inject a keV “seed” population into the inner magnetosphere which is subsequently energized through wave particle interactions up to relativistic energies; however, the extent to which substorms enhance the radiation belts, either directly or indirectly, has never before been quantified. In this study, we examine increases and decreases in the total radiation belt electron content (TRBEC) following substorms and geomagnetically quiet intervals. Our results show that the radiation belts are inherently lossy, shown by a negative median change in TRBEC at all intervals following substorms and quiet intervals. However, there are up to three times as many increases in TRBEC following substorm intervals. There is a lag of 1-3 days between the substorm or quiet intervals and their greatest effect on radiation belt content, shown in the difference between the occurrence of increases and losses in TRBEC following substorms and quiet intervals, the mean change in TRBEC following substorms or quiet intervals and the cross correlation between SuperMAG AL (SML) and TRBEC. However, there is a statistically significant effect on the occurrence of increases and decreases in TRBEC up to a lag of 6 days. Increases in radiation belt content show a significant correlation with SML and SYMH, but decreases in the radiation belt show no apparent link with magnetospheric activity levels.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2015-05-29
    Beschreibung: We report on features of solar wind-magnetosphere coupling elicited by shocks propagating through coronal mass ejections (CMEs) by analyzing the intense geomagnetic storm of August 6, 1998. During this event, the dynamic pressure enhancement at the shock combined with a simultaneous increase in the southward component of the magnetic field resulted in a large earthward retreat of Earth's magnetopause, which remained close to geosynchronous orbit for more than 4 hours. This occurred despite the fact that both shock and CME were weak and relatively slow. Another similar example of a weak shock inside a slow CME resulting in an intense geomagnetic storm is the September 30, 2012 event, which strongly depleted the outer radiation belt. We discuss the potential of shocks inside CMEs to cause large geomagnetic effects at Earth, including magnetopause shadowing.
    Print ISSN: 0094-8276
    Digitale ISSN: 1944-8007
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2019
    Beschreibung: Abstract Heterogeneous ice nucleating particle (INP) concentrations are reported for a site on the eastern margin of Beijing, China during the period 4 May – 4 June 2018. INP concentrations were measured continuously at ‐20, ‐25 and ‐30 °C in a repeating cycle by a newly developed, automated continuous flow diffusion chamber, and reached concentrations as high as 2800 sL‐1 during dust‐impacted periods. Study‐average concentrations were 70 ± 70, 230 ± 290 and 430 ± 500 sL‐1 at ‐20, ‐25, and ‐30 °C. There was no clear relationship between pollution periods, identified based on fine‐mode particle concentration increases, and INP concentrations or characteristics. Other anthropogenic emissions, such as non‐combustion industrial or agricultural activities play an unresolved role.
    Print ISSN: 2169-897X
    Digitale ISSN: 2169-8996
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2019
    Beschreibung: Abstract Electromagnetic ion cyclotron waves and fast magnetosonic waves are found to be simultaneously modulated by background plasma density: both kinds of waves were observed in high plasma density regions but vanished in low density regions. Theoretical analysis based on Snell's law and linear growth theory have been utilized to investigate the physical mechanisms driving such modulation. It is suggested that the modulation of fast magnetosonic waves might be due to trapping by plasma density structures, which results from a conservation of the parameter Q during their propagation. Here Q = nrsinψ, with n the refractive index, r the radial distance, and ψ the wave azimuthal angle. As for electromagnetic ion cyclotron waves, the modulation might be owed to the ion composition difference between different plasma density regions. Our results indicate the alternative mechanism for simultaneous appearance of electromagnetic ion cyclotron waves and fast magnetosonic waves (rather than wave excitations of both two wave emissions), which might take combined effects on the evolution of radiation belt electrons.
    Print ISSN: 2169-9380
    Digitale ISSN: 2169-9402
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2018-06-06
    Beschreibung: A method of using intense Laguerre–Gaussian (LG) laser pulse is proposed to generate ultrarelativistic (multi-GeV) electron beams with controllable helical structures based on a hybrid electron acceleration regime in underdense plasmas, where both the longitudinal charge-separation electric field and transverse laser electric field play the role of accelerating the electrons. By directly interacting with the LG laser pulse, the topological structure of the accelerated electron beam is manipulated and it is spatially separated into multi-slice helical bunches. These results are clearly demonstrated by our three-dimensional particle-in-cell simulations and explained by a theoretical model based on electron phase-space dynamics. This novel regime offers a new degree of freedom for manipulating ultrashort and ultrarelativistic electrons, and it provides an efficient way for generating high-energy high-angular-momentum helical electron beams, which may find applications in wide-rangi...
    Digitale ISSN: 1367-2630
    Thema: Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2018-10-12
    Beschreibung: Nitrogen and chlorine co-doped fluorescent carbon nanodots (CDs) were prepared using a facile and eco-friendly solvothermal process in which N-Chlorosuccinimide(NCS) was used as a carbon source. The resulting CDs were characterized by UV-visible absorption spectroscopy, fluorescence spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared and X-ray photoelectron spectroscopy (XPS). It shows emission of blue light at 410 nm when excited at 340 nm. High quantum yield of 21.7% and good biocompatibility were also observed. Importantly, the fluorescence intensity of CDs was selectively quenched after addition of Ag + . Based upon the aforementioned phenomenon, a new fluorescent biosensor for the detection of Ag + was proposed. The linear range and detection limit was 5-70 μM and 1.06 μM, respectively. Eventually, these superior properties demonstrated that the CDs have promising applications in the field of environmental a...
    Print ISSN: 1755-1307
    Digitale ISSN: 1755-1315
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2018-11-06
    Beschreibung: Changes in water resources are mainly affected by the combined effects of anthropogenic activities and climate change. The relative effects of anthropogenic activities and climate on a river basin are investigated to not only understand the hydrological response mechanism in a catchment but also manage local water resources and protect against floods and droughts. In this study, a variable infiltration capacity (VIC) model combined with a hydrologic sensitivity analysis was used to quantify the effects of anthropogenic activities and climate change on runoff in the upper reaches of the Hongshui River basin (UHRB). During 1970-2015, the runoff contribution for climate change and anthropogenic activities were 89.2% and 10.8%, respectively. This result suggests that climate is the major driver of runoff variation in the basin. However, during 1990-1999, anthropogenic activities played a decisive role in the reduction in streamflow, and the contribution percentage was 96.35%. Moreov...
    Print ISSN: 1755-1307
    Digitale ISSN: 1755-1315
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2017-09-01
    Beschreibung: The research of urban flood risk assessment and management are of great academic and practical importance, which has become a widespread concern throughout the world. It’s significant to understand the spatial-temporal distribution of the flood risk before making the risk response measures. In this study, the urban region of Jingdezhen City is selected as the study area. The assessment indicators are selected from four aspects: disaster-causing factors, disaster-pregnant environment, disaster-bearing body and the prevention and mitigation ability, by consideration of the formation process of urban flood risk. And then, a small-scale flood disaster risk assessment model is developed based on Analytic Hierarchy Process(AHP) and Geographic Information System(GIS), and the spatial-temporal distribution of flood risk in Jingdezhen City is analysed. The results show that the risk decreases gradually from the centre line of Changjiang River to the surrounding, and the areas of high flo...
    Print ISSN: 1755-1307
    Digitale ISSN: 1755-1315
    Thema: Geographie , Geologie und Paläontologie , Physik
    Standort Signatur Erwartet Verfügbarkeit
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