Strong-Field Many-Body Physics and the Giant Enhancement in the High-Harmonic Spectrum of Xenon

We resolve an open question about the origin of the giant enhancement in the high-harmonic generation (HHG) spectrum of atomic xenon around 100 eV. By solving the many-body time-dependent Schr\"odinger equation with all orbitals in the 4d, 5s, and 5p shells active, we demonstrate the enhancement results truly from collective many-body excitation induced by the returning photoelectron via two-body interchannel interactions. Without the many-body interactions, which promote a 4d electron into the 5p vacancy created by strong-field ionization, no collective excitation and no enhancement in the HHG spectrum exist.Comment: 5 pages, 4 figure

Introducing many-body physics using atomic spectroscopy

Atoms constitute relatively simple many-body systems, making them suitable objects for developing an understanding of basic aspects of many-body physics. Photoabsorption spectroscopy is a prominent method to study the electronic structure of atoms and the inherent many-body interactions. In this article the impact of many-body effects on well-known spectroscopic features such as Rydberg series, Fano resonances, Cooper minima, and giant resonances is studied, and related many-body phenomena in other fields are outlined. To calculate photoabsorption cross sections the time-dependent configuration interaction singles (TDCIS) model is employed. The conceptual clearness of TDCIS in combination with the compactness of atomic systems allows for a pedagogical introduction to many-body phenomena.Comment: 15 pages, 6 figures, 1 table. The following article has been accepted by American Journal of Physic

Driving Rabi oscillations at the giant dipole resonance in xenon

Free-electron lasers (FELs) produce short and very intense light pulses in the XUV and x-ray regimes. We investigate the possibility to drive Rabi oscillations in xenon with an intense FEL pulse by using the unusually large dipole strength of the giant-dipole resonance (GDR). The GDR decays within less than 30 as due to its position, which is above the $4d$ ionization threshold. We find that intensities around 10$^{18}$ W/cm$^2$ are required to induce Rabi oscillations with a period comparable to the lifetime. The pulse duration should not exceed 100 as because xenon will be fully ionized within a few lifetimes. Rabi oscillations reveal themselves also in the photoelectron spectrum in form of Autler-Townes splittings extending over several tens of electronvolt.Comment: 6 pages, 5 figure

Analysis of SUMO-protein modification and its effect on cellular processes

Conjugation of SUMO (small ubiquitin-related modifier) to a substrate protein is a posttranslational modification, which can have various consequences on the substrate’s activity, localization and stability. Structurally very similar to ubiquitin, SUMO is attached to a substrate in a similar enzymatic cascade, but in contrast, SUMO is not an immediate degradation signal for the substrate. However, ULS (ubiquitin ligases for sumoylated proteins) negatively regulate the abundance of SUMO conjugates by ubiquitylation which in turn leads to proteasomal degradation. Additionally, the desumoylating enzymes, in S. cerevisiae primarily Ulp2, negatively control the length of SUMO chains. Preliminary experiments from our laboratory have demonstrated that a failure in the control of sumoylation causes mitochondrial fragmentation. Dnm1 is the key enzyme for mitochondrial fission and it is known that sumoylation regulates the activity of its human ortholog Drp1. Motivated by these reports, a starting question was whether Dnm1 is sumoylated as well. In order to answer this question, various methods for the analysis of SUMO conjugates were established and applied. One of these methods was the application of cleavage-resistant SUMO variants, carrying the mutation Q95P, for the stabilization of these conjugates. Furthermore an optimized protocol for denaturing purification of SUMO and ubiquitin conjugates was established. In the following, this purification method was the basis for an approach to identify sumoylation sites by the application of the mass spectrometry optimized variant 8H-Smt3-KallR-I96R. In addition to identifying new SUMO substrates (for example the (Na+, K+)/H+ antiporter Vnx1), this analysis revealed N-terminal modification of SUMO, presumably by ubiquitin. From a more physiological point of view, the effect of the SUMO system on Dnm1 localization was investigated. Generation of a Ulp2 variant with a low-temperature degron and application of an improved mtGFP construct revealed that fragmentation of mitochondria occurs in the course of one day at restrictive temperature and is therefore probably a consequence of the accumulation of sumoylated proteins. Furthermore, it was discovered that specifically in the strain dnm1∆ fzo1∆, defective in mitochondrial dynamics, the absence of ULS leads to an increase in the formation of petite colonies. This in turn suggests that in particular in the absence of the mitochondrial quality control systems of fission and fusion, ULS are important to ensure respiratory competence. Regarding Dnm1 itself, a ubiquitylation of this protein could be demonstrated. However, at the same time under the applied conditions, a sumoylation of Dnm1 seems to be unlikely. Cdc11 could be successfully employed as a known SUMO substrate which confirmed the general capability of the applied methods. In agreement with the detection of ubiquitylated forms, it was found that Dnm1 is degraded via the ubiquitin-proteasome system. Furthermore, ethanol was discovered as a treatment that leads to degradation of Dnm1. Summarized, the methods established in the course of this study will be useful tools for the analysis of SUMO conjugates, and the finding of ubiquitylated Dnm1 could be a starting point for further analysis of this modification in respect to mitochondrial dynamics

Attosecond transient absorption of a bound wave packet coupled to a smooth continuum

We investigate the possibility to use transient absorption of a coherent bound electron wave packet in hydrogen as an attosecond pulse characterization technique. In recent work we have shown that photoionization of such a coherent bound electron wave packet opens up for pulse characterization with unprecedented temporal accuracy --- independent of the atomic structure --- with maximal photoemission at all kinetic energies given a wave packet with zero relative phase [Pabst and Dahlstr\"om, Phys. Rev. A, 94, 13411 (2016)]. Here, we perform numerical propagation of the time-dependent Schr\"odinger equation and analytical calculations based on perturbation theory to show that the energy-resolved maximal absorption of photons from the attosecond pulse does not uniquely occur at zero relative phase of the initial wave packet. Instead, maximal absorption occurs at different relative wave packet phases, distributed as a non-monotonous function with a smooth $-\pi/2$ shift across the central photon energy (given a Fourier-limited Gaussian pulse). Similar results are found also in helium. Our finding is surprising because it implies that the energy-resolved photoelectrons are not mapped one-to-one with the energy-resolved absorbed photons of the attosecond pulse.Comment: 10 pages, 8 figues, submitted as part of a Special Issue on Emerging Attosecond Technologies in Journal of Optic

The relationship between average color difference and 3-channel colorimetric quality factor for a simple additive color system

Neugebauer\u27s Colorimetric Quality Factor for a simple additive color reproduction system is calculated for 17 detector response functions. Each response function is used to simulate the reproduction of 124 colors and 774 metameric grays. The mean color difference between original and reproduced colors is calculated for colors and metamers for each detector response. The relationship between mean color difference and colorimetric Quality factor is studied

Controlling the 2p2p Hole Alignment in Neon via the 2s2s-3p3p Fano Resonance

We study the state-resolved production of neon ion after resonant photoionization of Ne via the $2s$-$3p$ Fano resonance. We find that by tuning the photon energy across the Fano resonance a surprisingly high control over the alignment of the final $2p$ hole along the polarization direction can be achieved. In this way hole alignments can be created that are otherwise very hard to achieve. The mechanism responsible for this hole alignment is the destructive interference of the direct and indirect (via the autoionizing $2s^{-1}3p$ state) ionization pathways of $2p$. By changing the photon energy the strength of the interference varies and $2p$-hole alignments with ratios up to 19:1 between $2p_0$ and $2p_{\pm 1}$ holes can be created: an effect normally only encountered in tunnel ionization using strong-field IR pulses. Including spin-orbit interaction does not change the qualitative feature and leads only to a reduction in the alignment by $2/3$. Our study is based on a time-dependent configuration-interaction singles (TDCIS) approach which solves the multichannel time-dependent Schr\"odinger equation.Comment: 7 pages, 4 figure

Sozialpolitische Entscheidungsprozesse in der Bundesrepublik Deutschland zwischen 1982 und 1989: Eine Literaturübersicht

In diesem Arbeitspapier werden die vorliegenden Forschungsergebnisse über die Willensbildungs- und Entscheidungsprozesse in der Sozialpolitik der Bundesrepublik Deutschland zwischen 1982 und 1989 zusammenfassend dargestellt. Dazu wird zunächst die Entwicklung in den einzelnen Politikfeldern nachgezeichnet. Daraufhin wird politikfeldübergreifend der Frage nachgegangen, welche Schlüsselvariablen die Gesetzgebungsprozesse beeinflußt haben und das von der Regierung Kohl angestrebte Ziel der finanziellen Konsolidierung und institutionellen Reform des deutschen Sozialstaates blockierten bzw. ermöglichten. Die vorliegenden Studien kommen einerseits zu dem (wenig überraschenden) Ergebnis, daß in den sozialpolitischen Entscheidungsprozessen zwischen 1982 und 1989 die 'klassischen' Institutionen wie der Bundesrat, das Bundesverfassungsgericht oder die Interessenverbände Einfluß auf die Regierungspolitik nehmen konnten. Andererseits weisen die Gesetzgebungsprozesse in der ersten Hälte der 'Ära Kohl' auch einige Besonderheiten auf: Dazu zählt, daß die Konflikte innerhalb der CDU in diesem Zeitraum ein großes Gewicht für die Ausgestaltung der Sozialpolitik aufwiesen, und daß es der Regierung gelang, durch ein spezifisches Politikmanagent die Einflußmöglichkeiten ihrer Opponenten zu verringern. --