Multiple-ionization of xenon atoms by positron impact

Previously the cross sections were measured for positronium formation and single ionization by positron impact for He and H2. With the same apparatus, slightly modified, the single and multiple ionization of xenon is now investigated. The principle of the method is the detection of ion and positron in time correlation which allows the discrimination of positronium formation (whereby the positron vanishes) and the destinction of single, double and triple impact ionization (which lead to different ion flight times from the gas target to the ion detector). By using secondary electrons from the positron moderator, similar measurements were performed on electron impact ionization. By comparing with literature values for electron multiple ionization cross sections, the detection-probability ratios were determined for the differently charged ions

Lorentz meets Fano spectral line shapes: A universal phase and its laser control

Symmetric Lorentzian and asymmetric Fano line shapes are fundamental spectroscopic signatures that quantify the structural and dynamical properties of nuclei, atoms, molecules, and solids. This study introduces a universal temporal-phase formalism, mapping the Fano asymmetry parameter q to a phase {\phi} of the time-dependent dipole-response function. The formalism is confirmed experimentally by laser-transforming Fano absorption lines of autoionizing helium into Lorentzian lines after attosecond-pulsed excitation. We also prove the inverse, the transformation of a naturally Lorentzian line into a Fano profile. A further application of this formalism amplifies resonantly interacting extreme-ultraviolet light by quantum-phase control. The quantum phase of excited states and its response to interactions can thus be extracted from line-shape analysis, with scientific applications in many branches of spectroscopy.Comment: 11 pages, 4 figure

Amnion cells engineering: A new perspective in fetal membrane healing after intrauterine surgery?

In this study we aimed to set up an in vitro culture of the rabbit amnion in order to support in vivo fetal membrane healing capacity following fetoscopy. Fetal membranes were collected from a mid- gestational rabbit, and cultured on collagen support material for 14 days. 34 rabbits at 22 - 23 days gestational age ( GA) underwent fetoscopy. The entry site was randomly allocated to 4 closure technique study groups: group I, human amnion membrane ( n = 23); group II, collagen foil ( n = 16); group III, collagen plug ( n = 19), and group IV, collagen plug with cultured amnion cells ( n = 19). In all groups membrane access sites were additionally sealed with fibrin sealant, and the myometrium was closed with sutures. Fetal survival, amnion membrane integrity, and the presence of amniotic fluid were evaluated at 30 days GA. Cultures showed good survival in the collagen support material. Increased cellularity, survival and proliferations were observed. The amnion at the access site resealed in 58 - 64% of cases in groups II - IV, but none of the tested techniques was significantly better than the other. Histological examination indirectly revealed the anatomic repair of the membranes, since no entrapment of the membranes could be demonstrated in the myometrial wound. Copyright (c) 2006 S. Karger AG, Basel

Reconstruction and control of a time-dependent two-electron wave packet

The concerted motion of two or more bound electrons governs atomic1 and molecular2,3 non-equilibrium processes including chemical reactions, and hence there is much interest in developing a detailed understanding of such electron dynamics in the quantum regime. However, there is no exact solution for the quantumthree-body problem, and as a result even the minimal system of two active electrons and a nucleus is analytically intractable4. This makes experimental measurements of the dynamics of two bound and correlated electrons, as found in the helium atom, an attractive prospect.However, although the motion of single active electrons and holes has been observed with attosecond time resolution5-7, comparable experiments on two-electron motion have so far remained out of reach. Here we showthat a correlated two-electron wave packet can be reconstructed froma 1.2-femtosecondquantumbeatamong low-lying doubly excited states in helium.The beat appears in attosecond transient-absorption spectra5,7-9 measured with unprecedentedly high spectral resolution and in the presence of an intensity-tunable visible laser field.Wetune the coupling10-12 between the two low-lying quantum states by adjusting the visible laser intensity, and use the Fano resonance as a phase-sensitive quantum interferometer13 to achieve coherent control of the two correlated electrons. Given the excellent agreement with large-scalequantum-mechanical calculations for thehelium atom, we anticipate thatmultidimensional spectroscopy experiments of the type we report here will provide benchmark data for testing fundamental few-body quantumdynamics theory in more complex systems. Theymight also provide a route to the site-specificmeasurement and control of metastable electronic transition states that are at the heart of fundamental chemical reactionsWe thank E. Lindroth for calculating the dipole moment (2p2|r|sp2,3+), and also A. Voitkiv, Z.-H. Loh, and R. Moshammer for helpful discussions. We acknowledge financial support by the Max-Planck Research Group Program of the Max-Planck Gesellschaft (MPG) and the European COST Action CM1204 XLIC. L. A. and F. M. acknowledge computer time from the CCC-UAM and Mare Nostrum supercomputer centers and financial support by the European Research Council under the ERC Advanced Grant no. 290853 XCHEM, the Ministerio de Economía y Competitividad projects FIS2010-15127, FIS2013-42002-R and ERA-Chemistry PIM2010EEC-00751, and the European grant MC-ITN CORIN

Informal nature experience on the school playground

In Germany, all-day care and all-day schooling are currently increasing on a large-scale. The extended time children spend in educational institutions could potentially result in limited access to nature experience for children. On the other hand, it could equally create opportunities for informal nature experience if school playgrounds have a specific nature-oriented design. This article is written from the perspective of a primary school teacher and presents the findings of a meta-analysis which looks at the impact nature experience has on the development of children. Furthermore, the first results of a research study on green playgrounds in primary schools is discussed. The results so far seem to indicate that green school playgrounds have the potential of providing nature experience particularly for primary student

Das Potential naturnah gestalteter Schulhöfe für informelle Naturerfahrungen

Das Ziel dieser Studie war, das Potential von naturnah gestalteten Schulhöfen für informelle Naturerfahrungen zu untersuchen. Dazu wurde zunächst der aktuelle Forschungsstand zum Einfluss von Naturerfahrungen auf die kindliche Entwicklung geprüft. Dann wurde empirisch untersucht, in wie weit Naturkontakt auf naturnah gestalteten Schulhöfen stattfindet und ob dieser Naturkontakt auch zu Naturerfahrungen führt. Die Studie war aufgeteilt in eine theoretische und drei empirische Phasen. Zunächst wurde eine ausführliche Literaturrecherche zum Einfluss von Naturerfahrungen auf die kindliche Entwicklung durchgeführt. Aus dieser Recherche wurden die Problemstellung der Studie und die übergeordneten Fragestellungen zur Nutzung der naturnah gestalteten Schulhöfe und der auf ihnen stattfindenden Naturerfahrungen entwickelt. Darauf folgte die erste empirische Phase. Über Beobachtungen auf einem naturnah gestalteten Schulhof wurde qualitativ untersucht, welche Aktivitäten dort vorkamen und ob es potentielle Zusammenhänge zwischen den Aktivitäten der Kinder und dem Schulhofsetting, dem Geschlecht und dem Alter der Kinder geben könnte. Die Beobachtungen zeigten Hinweise auf Naturkontakte auf dem Schulhof in zwei verschiedenen Dimensionen, einer Umgebungsdimension und einer Handlungsdimension, außerdem schienen Altersunterschiede bei der Häufigkeit von Naturkontakt auf dem Schulhof vorzuliegen. Aus diesen Erkenntnissen wurden Hypothesen zu Einflussfaktoren auf den Naturkontakt auf naturnah gestalteten Schulhöfen für die weitere Untersuchung abgeleitet. In der zweiten empirischen Phase wurden die gestellten Hypothesen über Beobachtungen quantitativ geprüft. Dazu wurden 71 Beobachtungen auf Schulhöfen durchgeführt und quantitativ ausgewertet. Dabei zeigten sich signifikante Alterseffekte. Je jünger die Kinder sind, desto häufiger haben sie auf dem Schulhof Naturkontakt. Vegetationsdichte und Geländestrukturierung hatten nur geringen Einfluss. Allerdings konnten funktionale Ausstattungsmerkmale (z.B. eine Sitzgelegenheit oder eine Rutsche) bestimmt werden, die positiven oder negativen Einfluss auf den Naturkontakt spezifisch für Altersgruppen haben. In der dritten empirischen Phase wurden mit Interviews die Häufigkeit und die Arten von Naturerfahrungen qualitativ untersucht. Außerdem wurden kausale Zusammenhänge zur Nutzung von naturnahen Schulhofbereichen und zu Kohorteneffekten geprüft. Es traten auch hier Alterseffekte zu Tage. Jüngere Kinder bevorzugten naturnahe Schulhofbereiche, ältere Kinder naturferne. Naturkontakt lag nicht im Fokus der Aktivitäten der Kinder. Dennoch berichteten sie von Naturerfahrungen, die bei jüngeren Kindern und bei Mädchen häufiger vorkamen. Die aufgetretenen Naturerfahrungen waren vor allem passiver Natur