MAY I HAVE YOUR ATTENTION, PLEASE? – THE INTERACTION BETWEEN ATTENTION SCREENING AND REPUTATION ON CROWDWORKING PLATFORMS

Our study aims to better understand attention screening mechanisms (‘screeners’) on crowdworking platforms, and their consequences on worker behavior. Crowdworking platforms are popular with researchers conducting online experiments, but are associated with pitfalls that have come under increasing scientific scrutiny, such as the quality of contributions due to the limited attention span or the uncontrolled environment of crowdworkers. While screeners can be built into tasks to check for attention, and crowdworking platforms are implementing reputation management systems for workers, based upon the quality of their contributions, two main questions arise: 1) which screener types are best suited to ensure high attentiveness, and 2) how does a possible interaction between screeners and workers’ eagerness to maintain their reputation affect online research? To address both questions, we propose a two-stage experimental design to compare different screener types regarding their ability to guarantee high attentiveness and their potential interaction with reputation systems

Photoionization in strong laser fields: from atoms to complex molecules

In this thesis, the results of the strong-field photoionization of various gas targets, particularly of methane are presented. The photoionization was performed by focusing an ultrashort two-color laser pulse into the supersonic gas jet of a Reaction Microscope. The capability of the Reaction Microscope of simultaneous detection and identification of all charged ionization products enables the channel- and fragment-specific analysis of the ionization process. The tunable relative phase between both components of the two-color field is an additional control parameter for the experiment. The discrepancy in the yield of lowenergy photoelectrons for methane ionization channels with a coincident molecular ion on the one hand and a coincident atomic ion on the other hand resembles similar results from experiments in molecular hydrogen, which could be explained by autoionization and simultaneous vibrational relaxation of a molecular Rydberg state. Despite the lack of reference data for Rydberg states of methane with excitations higher than n = 6, it was possible to estimate their energies and for one ionization channel, it could be demonstrated that electrons released by autoionization of Rydberg states between n = 9 and n = 12 are the origin of the enhanced low-energy electron yield

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

Experimental evidence for Wigner's tunneling time

Tunneling of a particle through a potential barrier remains one of the most remarkable quantum phenomena. Owing to advances in laser technology, electric fields comparable to those electrons experience in atoms are readily generated and open opportunities to dynamically investigate the process of electron tunneling through the potential barrier formed by the superposition of both laser and atomic fields. Attosecond-time and angstrom-space resolution of the strong laser-field technique allow to address fundamental questions related to tunneling, which are still open and debated: Which time is spent under the barrier and what momentum is picked up by the particle in the meantime? In this combined experimental and theoretical study we demonstrate that for strong-field ionization the leading quantum mechanical Wigner treatment for the time resolved description of tunneling is valid. We achieve a high sensitivity on the tunneling barrier and unambiguously isolate its effects by performing a differential study of two systems with almost identical tunneling geometry. Moreover, working with a low frequency laser, we essentially limit the non-adiabaticity of the process as a major source of uncertainty. The agreement between experiment and theory implies two substantial corrections with respect to the widely employed quasiclassical treatment: In addition to a non-vanishing longitudinal momentum along the laser field-direction we provide clear evidence for a non-zero tunneling time delay. This addresses also the fundamental question how the transition occurs from the tunnel barrier to free space classical evolution of the ejected electron.Comment: 31 pages, 15 figures including appendi

Wall turbulence at high friction Reynolds numbers

[EN] A new direct numerical simulation of a Poiseuille channel flow has been conducted for a friction Reynolds number of 10000, using the pseudospectral code LISO. The mean streamwise velocity presents a long logarithmic layer, extending from 400 to 2500 wall units, longer than it was thought. The maximum of the intensity of the streamwise velocity increases with the Reynolds number, as expected. Also, the elusive second maximum of this intensity has not appeared yet. In case it exists, its location will be around y(+) approximate to 120, for a friction Reynolds number extrapolated to approximately 13 500. The small differences in the near-wall gradient of this intensity for several Reynolds numbers are related to the scaling failure of the dissipation, confirming this hypothesis. The scaling of the turbulent budgets in the center of the channel is almost perfect above 1000 wall units. Finally, the peak of the pressure intensity grows with the Reynolds number and does not scale in wall units. If the pressure at the wall is modeled as an inverse quadratic power of Re-tau, then p(infinity)'(+) approximate to 4.7 at the limit of infinite Reynolds number.The authors gratefully acknowledge computing time provided by the Gauss Centre for Supercomputing e.V. on the GCS Supercomputer SuperMUC-NG at Leibniz Supercomputing Centre under Project No. pr92la, on the supercomputer Lichtenberg II at TU Darmstadt under Project No. project00072, and on the supercomputer CLAIX-2018 at RWTH-Aachen, Project No. bund0008. We are thankful to Mr. Monkewitz for providing us a copy of his model. S.K. and M.O. acknowledge funding by the German Research Foundation (DFG) through the Project No. OB96/39-1 and OB96/48-1. S.H. and F.A.A. were supported by Contract No. RTI2018-102256-B-I00 of MINECO/FEDER. F.A.A. is partially funded by GVA/FEDER Project No. ACIF2018. Finally, the authors thank Paul Hollmann for corrections with Latex.Hoyas, S.; Oberlack, M.; Alcántara-Ávila, F.; Kraheberger, SV.; Laux, J. (2022). Wall turbulence at high friction Reynolds numbers. Physical Review Fluids. 7(1):1-10. https://doi.org/10.1103/PhysRevFluids.7.0146021107

Turbulence Statistics of Arbitrary Moments of Wall-Bounded Shear Flows: A Symmetry Approach

[EN] The calculation of turbulence statistics is considered the key unsolved problem of fluid mechanics, i.e., precisely the computation of arbitrary statistical velocity moments from first principles alone. Using symmetry theory, we derive turbulent scaling laws for moments of arbitrary order in two regions of a turbulent channel flow. Besides the classical scaling symmetries of space and time, the key symmetries for the present work reflect the two well-known characteristics of turbulent flows: non-Gaussianity and intermittency. To validate the new scaling laws we made a new simulation at an unprecedented friction Reynolds number of 10 000, large enough to test the new scaling laws. Two key results appear as an application of symmetry theory, which allowed us to generate symmetry invariant solutions for arbitrary orders of moments for the underlying infinite set of moment equations. First, we show that in the sense of the generalization of the deficit law all moments of the streamwise velocity in the channel center follow a power-law scaling, with exponents depending on the first and second moments alone. Second, we show that the logarithmic law of the mean streamwise velocity in wall-bounded flows is indeed a valid solution of the moment equations, and further, all higher moments in this region follow a power law, where the scaling exponent of the second moment determines all higher moments. With this we give a first complete mathematical framework for all moments in the log region, which was first discovered about 100 years ago.The authors gratefully acknowledge computing time on the Gauss Centre for Supercomputing e.V. on the GCS Supercomputer SuperMUC-NG at Leibniz Supercomputing Centre under Project No. pr92la, on the supercomputer Lichtenberg II at TU Darmstadt under Project No. project00072, and on the supercomputer CLAIX-2018 at RWTH-Aachen under Project No. bund0008. S. V. K. gratefully acknowledges funding from projects OB96/39-1 and M. O. for partial funding from OB 96/48-1, both financed by the German Research Foundation (DFG) . S. H. and F. A.-A. were supported by Contract No. RTI2018-102256-B-I00 of Ministerio de Ciencia, innovacion y Universidades/FEDER. F. A.-A. is partially funded by GVA/FEDER project ACIF2018. Finally, the authors thank Paul Hollmann for help with the manuscript.Oberlack, M.; Hoyas, S.; Kraheberger, SV.; Alcántara-Ávila, F.; Laux, J. (2022). Turbulence Statistics of Arbitrary Moments of Wall-Bounded Shear Flows: A Symmetry Approach. Physical Review Letters. 128(2):1-6. https://doi.org/10.1103/PhysRevLett.128.02450216128

Task acquisition with a description logic reasoner

In many knowledge based systems the application domain is modeled in an object-centered formalism. Research in knowledge acquisition has given evidence that this approach allows one to adequately model the conceptual structures of human experts. However, when a novice user wants to describe a particular task to be solved by such a system he has to be well acquainted with the underlying domain model, and therefore is charged with the burden of making himself familiar with it. We aim at giving automated support to a user in this process, which we call task acquisition. This paper describes the TACOS system, which guides a user through an object-centered domain model and gives support to him in specifying his task. A characteristic of TACOS is that the user can enter only information that is meaningful and consistent with the domain model. In order to identify such information, TACOS exploits the ability of a description logic based knowledge representation system to reason about such models

PMAS: The Potsdam Multi Aperture Spectrophotometer. II. The Wide Integral Field Unit PPak

PPak is a new fiber-based Integral Field Unit (IFU), developed at the Astrophysical Institute Potsdam, implemented as a module into the existing PMAS spectrograph. The purpose of PPak is to provide both an extended field-of-view with a large light collecting power for each spatial element, as well as an adequate spectral resolution. The PPak system consists of a fiber bundle with 331 object, 36 sky and 15 calibration fibers. The object and sky fibers collect the light from the focal plane behind a focal reducer lens. The object fibers of PPak, each 2.7 arcseconds in diameter, provide a contiguous hexagonal field-of-view of 74 times 64 arcseconds on the sky, with a filling factor of 60%. The operational wavelength range is from 400 to 900nm. The PPak-IFU, together with the PMAS spectrograph, are intended for the study of extended, low surface brightness objects, offering an optimization of total light-collecting power and spectral resolution. This paper describes the instrument design, the assembly, integration and tests, the commissioning and operational procedures, and presents the measured performance at the telescope.Comment: 14 pages, 21 figures, accepted at PAS