1,739 research outputs found
Nanoplasmonic near-field synthesis
The temporal response of resonances in nanoplasmonic structures typically
converts an incoming few-cycle field into a much longer near-field at the spot
where non-linear physical phenomena including electron emission, recollision
and high-harmonic generation can take place. We show that for practically
useful structures pulse shaping of the incoming pulse can be used to synthesize
the plasmon-enhanced field and enable single-cycle driven nonlinear physical
phenomena. Our method is demonstrated for the generation of an isolated
attosecond pulse by plasmon-enhanced high harmonic generation. We furthermore
show that optimal control techniques can be used even if the response of the
plasmonic structure is not known a priori.Comment: 6 page
Biodiversity, distribution and patterns of extinction of the last odontopleurid tilobites during the Devonian (Givetian, Frasnian)
Biostratigraphical ranges and palaeogeographical distribution of mid-Givetian to end-Frasnian odontopleurids are investigated. The discovery of Leonaspis rhenohercynica sp. nov. in mid-Givetian strata extends this genus unexpectedly up to the late Middle Devonian. New material of Radiaspis radiata (Goldfuss, 1843) and the first koneprusiine in Britain, Koneprusia? sp., are described from the famous Lummaton shell-bed, Torquay, Devon. New taxa of Koneprusia, K. serrensis, K. aboussalamae, K. brevispina, and K. sp. A and K. sp. B are defined. Ceratocephala (Leonaspis) harborti Richter & Richter, 1926, is revised and reassigned to Gondwanaspis Feist, 2002. Two new species of Gondwanaspis, G. dracula and G. spinosa, plus three others left in open nomenclature, are described from the late Frasnian of Western Australia. A further species of Gondwanaspis, G. prisca, is described from the early Frasnian of Montagne Noire. Species of Gondwanaspis are shown to possess a number of paedomorphic features. A functional analysis suggests that, unlike other odontopleurids, Gondwanaspis actively fed and rested with the same cephalic orientation. The sole odontopleurid survivors of the severe terminal mid-Givetian biocrisis (‘Taghanic Event’) belong to the koneprusiine Koneprusia in the late Givetian and Frasnian, and, of cryptogenic origin, the acidaspidine Gondwanaspis in the Frasnian. Whereas the former became extinct in the late Frasnian at the Lower Kellwasser Event, the latter disappeared, and with it the entire Odontopleuroidea, at the terminal Frasnian Upper Kellwasser global biocrisis
Viola rafinesquii Greene
https://thekeep.eiu.edu/herbarium_specimens_byname/20665/thumbnail.jp
Viola rafinesquii Greene
https://thekeep.eiu.edu/herbarium_specimens_byname/20665/thumbnail.jp
Phoradendron leucarpum (Raf.) Reveal & M.C. Johnston
https://thekeep.eiu.edu/herbarium_specimens_byname/16418/thumbnail.jp
Probing Electron Correlation via Attosecond XUV Pulses in the Two-Photon Double Ionization of Helium
Recent experimental developments of high-intensity, short-pulse XUV light
sources are enhancing our ability to study electron-electron correlations. We
perform time-dependent calculations to investigate the so-called "sequential"
regime (photon energy above 54.4 eV) in the two-photon double ionization of
helium. We show that attosecond pulses allow to induce and probe angular and
energy correlations of the emitted electrons. The final momentum distribution
reveals regions dominated by the Wannier ridge break-up scenario and by
post-collision interaction.Comment: 4 pages, 5 figure
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