171,291 research outputs found
Stimulus-driven brain oscillations in the alpha range: entrainment of intrinsic rhythms or frequency-following response?
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Reformen des Mathematikunterrichts in den USA: Geschichte, Reformkonzeptionen und Curriculumentwicklung
No full textKeitel-Kreidt C. Reformen des Mathematikunterrichts in den USA: Geschichte, Reformkonzeptionen und Curriculumentwicklung. Bielefeld; 1982
Wanderungen durch die Mark Brandenburg
No full textErhart W. Wanderungen durch die Mark Brandenburg. In: Grawe C, Keitel W, eds. Fontane-Handbuch. Stuttgart: Kröner; 2000: 818-850
Beyond the Tunnel Vision:Analysing the Relationship Between Mathematics, Society and Technology
No full textCounseling Women With Breast Cancer : A guide For Profesionals/ Keitel
No full textXIV, 176 hal. : tab. ; 23 c
Counseling Women With Breast Cancer : A guide For Profesionals/ Keitel
No full textXIV, 176 hal. : tab. ; 23 c
Counseling Women With Breast Cancer : A guide For Profesionals/ Keitel
No full textXIV, 176 hal. : tab. ; 23 c
Streaking at high energies with electrons and positrons
No full textState-of-the-art attosecond metrology deals with the detection and characterization of photon pulses with typical energies up to the hundreds of eV and time resolution of several tens of attoseconds [1]. Such short pulses are used for example to control the motion of electrons on the atomic scale or to measure inner-shell atomic dynamics. The next challenge of time-resolving the inner-nuclear dynamics, transient meson states and resonances requires photon pulses below attosecond duration and with energies exceeding the MeV scale [2,3].
In this talk, we present a detection scheme for time-resolving high-energy gamma ray pulses down to the zeptosecond timescale [4]. The scheme is based on the concept of attosecond streak imaging, but instead of conversion of photons into electrons in a nonlinear medium, the high-energy process of electron-positron pair creation is utilized. These pairs are produced in vacuum through the collision of a test pulse to be characterized with an intense laser pulse, and they acquire additional energy and momentum depending on their phase in the streaking pulse at the moment of production. A coincidence measurement of the electron and positron momenta after the interaction provides information on the pair production phase within the streaking pulse. We examine the limitations imposed by quantum radiation reaction in multiphoton Compton scattering on this detection scheme [5], and discuss other necessary conditions to render the scheme feasible in the upcoming Extreme Light Infrastructure (ELI) laser facility.
[1] F. Krausz, M. Ivanov, Rev. Mod. Phys. 81:163, 2009.
[2] A. Ipp, C. H. Keitel, J. Evers, Phys. Rev. Lett. 103:152301, 2009.
[3] A. Ipp, A. Di Piazza, J. Evers, C. H. Keitel, Phys. Lett. B 666:315, 2008.
[4] A. Ipp, J. Evers, C. H. Keitel, and K. Z. Hatsagortsyan, Phys. Lett. B 702:383, 2011.
[5] A. Di Piazza, K. Z. Hatsagortsyan, and C. H. Keitel, Phys. Rev. Lett. 105:220403, 2010
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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