X-ray high-resolution diffraction using refractive lenses

Refractive x-ray lenses have recently been applied for imaging and scanning microscopy with hard x rays. We report the application of refractive lenses in an optical scheme for high-resolution x-ray diffraction, performed at a high brilliance synchrotron radiation source. An experimental proof of principle and a theoretical discussion are presented. In particular, we observe the x-ray diffraction pattern from a two-dimensional photonic crystal with 4.2 µm periodicity, which normally is employed to scatter light in the infrared

Towards reproducible research of event detection techniques for Twitter

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Enhancing the knowledge about faking : ability, motivation, and beyond

The use of self-assessment tools (such as personality tests or job interviews) for personnel selection always carries the risk that in order to increase their chances of selection, applicants will not answer honestly. This intentional distortion of answers – known as faking – can have a significant impact on selection decisions and can jeopardize the validity of selection procedures. In recent decades, these highly problematic consequences of faking for organizations have regularly brought the phenomenon into scientific focus. However, despite extensive theoretical and empirical research in this area, there are still a number of unanswered questions regarding the emergence and consequences of faking. Therefore, the aim of my dissertation is to further contribute to the understanding of this highly relevant phenomenon inherent in personnel selection, by looking at two of the currently unresolved research issues in this area. In a first step, I focused on the long-unanswered question of whether cognitive abilities are an important determinant of faking behavior. The results of my meta-analysis suggest that cognitive abilities play a decisive role for successful applicant faking in personality tests. However, significant differences between the results of laboratory and field studies also revealed evidence of different underlying mechanisms in the two research contexts. In the second study, I used an approach from the field of socioecological psychology to examine the motivational effects of competition on applicants’ faking in the interview context. While hard economic indicators of competition showed no effects, both the individual and the regionally shared attitudes towards competition emerged as important predictors of faking. Finally, I brought together the two previously studied aspects in a comprehensive laboratory study with three large samples and different operationalizations of the corresponding variables. However, the results did not support the expected effects of applicants’ cognitive abilities or their attitudes towards competition. In fact, this study, like the first one, provided evidence that instructed faking in the laboratory environment is governed by slightly different mental and motivational processes than faking in real application situations. All things considered, my dissertation provides important insights into both the motivational and the ability aspect of faking, but it also underlines that the processes occurring in applicants’ minds may be more complex and possibly also more difficult to reproduce in the laboratory than previously assumed. Accordingly, my dissertation calls for more research on the concrete mental processes of applicants in real selection situations as well as for a critical debate about the usefulness of laboratory studies in faking research.Werden Selbstauskunftsverfahren (z.B. Persönlichkeitstests oder Vorstellungsgespräche) zur Personalauswahl eingesetzt, besteht immer die Gefahr, dass Bewerber nicht ehrlich antworten, um ihre Auswahlchancen zu erhöhen. Dieses beabsichtigte Verzerren von Antworten, welches als Faking bezeichnet wird, kann einen konkreten Einfluss auf Auswahlentscheidungen haben und damit die Validität eignungsdiagnostischer Verfahren gefährden. Aufgrund dieser problematischen Auswirkungen, ist Faking bereits seit Jahrzehnten immer wieder im Fokus der Personalauswahlforschung. Allerdings bleiben bisher trotz umfangreicher theoretischer und empirischer Arbeiten in diesem Bereich noch einige Aspekte der Entstehung und Folgen von Faking ungeklärt. Ziel meiner Dissertation ist es, weiter zum Verständnis dieses hochrelevanten Phänomens der Personalauswahl beizutragen und zwei der aktuellen Themen dieses Forschungsbereichs zu untersuchen. Dazu konzentriere ich mich in einem ersten Schritt auf die seit Langem unbeantwortete Frage, ob kognitive Fähigkeiten eine wichtige Determinante von Faking sind. Die Ergebnisse meiner Meta-Analyse deuten darauf hin, dass kognitive Fähigkeiten tatsächlich eine entscheidende Rolle für erfolgreiches Faking von Persönlichkeitstests spielen. Erhebliche Unterschiede zwischen den Ergebnissen von Labor- und Feldstudien geben dabei aber auch Hinweise auf unterschiedliche zugrunde liegende Mechanismen in beiden Forschungskontexten. In einer zweiten Studie untersuche ich mit einem aus der sozialökologischen Psychologie entliehenen Ansatz die motivationalen Auswirkungen von Wettbewerb auf Bewerberfaking im Interviewkontext. Während in dieser Studie harte wirtschaftliche Indikatoren von Wettbewerb keine Effekte zeigen, sind sowohl die individuelle als auch die regional geteilte Einstellung bezüglich Wettbewerbes wichtige Prädiktoren für Faking. Wieder im Rahmen von Persönlichkeitstests bringe ich schließlich die beiden zuvor untersuchten Aspekte in einer umfangreichen Laborstudie mit drei großen Stichproben und unterschiedlichen Operationalisierungen der Variablen zusammen. Allerdings zeigt sich hier weder der erwartete Einfluss der kognitiven Fähigkeiten noch der Einstellung zu Wettbewerb auf Faking. Vielmehr liefert diese Studie, wie auch schon die erste, Hinweise darauf, dass instruiertes Faking im Laborkontext von anderen mentalen und motivationalen Prozessen gesteuert wird als Faking in realen Auswahlsituationen. In ihrer Gesamtheit liefert meine Dissertation wichtige Erkenntnisse über den Motivations- und Fähigkeitsaspekt von Bewerberfaking, weist aber auch darauf hin, dass die Prozesse, die in den Köpfen der Bewerber ablaufen, komplexer und möglicherweise auch schwieriger im Labor reproduzierbar sind, als bisher angenommen. Entsprechend ruft meine Dissertation zu mehr Forschung über die konkreten mentalen Prozesse von Bewerbern in echten Auswahlsituationen auf und fordert eine kritische Auseinandersetzung mit der Nützlichkeit von Laborstudien für die Fakingforschung

SU(2) Colour Fields Around Static Sources

First results of an ongoing high statistics study of the colour flux distribution around static quark sources in SU(2) gauge theory are presented. The flux tube profiles and widths have been investigated for several quark separations at beta=2.5 and beta=2.74. The results are tested against Michael's sum rules.Comment: 3 pages (LaTeX) with 4 epsf incl. PS figs., To be publ. in Proc. of Lattice '9

Superconducting fluctuations in a thin NbN film probed by the Hall effect

We present a comprehensive study of how superconducting fluctuations in the normal state contribute to the conductivity tensor in a thin (119 $\AA$) film of NbN. It is shown how these fluctuations drive a sign change in the Hall coefficient $R_\mathrm{H}$ for low magnetic fields near the superconducting transition. The scaling behaviours as a function of distance to the transition $\epsilon=\ln(T/T_\mathrm{c})$ of the longitudinal ($\sigma_\mathrm{xx}$) and transverse ($\sigma_\mathrm{xy}$) conductivity is found to be consistent with Gaussian fluctuation theory. Moreover, excellent quantitative agreement between theory and experiment is obtained without any adjustable parameters. Our experimental results thus provide a case study of the conductivity tensor originating from short-lived Cooper pairs.Comment: 6 pages, 4 figure

The Running Coupling from SU(3) Gauge Theory

We present high precision results on the static quark-antiquark-potential on 32^4 and smaller lattices, using the standard Wilson action at BETA = 6.0, 6.2, 6.4, and 6.8 on the Connection Machine CM-2. Within our statistical errors (1%) we did not observe any finite size effects affecting the potential values, on varying the spatial lattice extent from 0.9 fm up to 3.3 fm. We find violations of asymptotic scaling in the bare coupling up to BETA = 6.8. We demonstrate that scaling violations on the string tension can be considerably reduced by introducing effective coupling schemes, which allow for a safer extrapolation of LAMBDA_Lattice to its continuum value. We are also able to see and to quantify the running of the coupling from the interquark force. From this we extract the ratio \sqrt{SIGMA}/LAMBDA_L. Both methods yield consistent values for the LAMBDA-parameter: LAMBDA_MSbar = 0.558(-0.007+0.017)\sqrt{SIGMA} = 246(-3+7) MeV.Comment: (Talk G. Bali at Lattice 92, Amsterdam), 4 Pages, 4 Postscript figures, LaTeX with espcrc2, and epsf style file

Microscopic theory of glassy dynamics and glass transition for molecular crystals

We derive a microscopic equation of motion for the dynamical orientational correlators of molecular crystals. Our approach is based upon mode coupling theory. Compared to liquids we find four main differences: (i) the memory kernel contains Umklapp processes, (ii) besides the static two-molecule orientational correlators one also needs the static one-molecule orientational density as an input, where the latter is nontrivial, (iii) the static orientational current density correlator does contribute an anisotropic, inertia-independent part to the memory kernel, (iv) if the molecules are assumed to be fixed on a rigid lattice, the tensorial orientational correlators and the memory kernel have vanishing l,l'=0 components. The resulting mode coupling equations are solved for hard ellipsoids of revolution on a rigid sc-lattice. Using the static orientational correlators from Percus-Yevick theory we find an ideal glass transition generated due to precursors of orientational order which depend on X and p, the aspect ratio and packing fraction of the ellipsoids. The glass formation of oblate ellipsoids is enhanced compared to that for prolate ones. For oblate ellipsoids with X <~ 0.7 and prolate ellipsoids with X >~ 4, the critical diagonal nonergodicity parameters in reciprocal space exhibit more or less sharp maxima at the zone center with very small values elsewhere, while for prolate ellipsoids with 2 <~ X <~ 2.5 we have maxima at the zone edge. The off-diagonal nonergodicity parameters are not restricted to positive values and show similar behavior. For 0.7 <~ X <~ 2, no glass transition is found. In the glass phase, the nonergodicity parameters show a pronounced q-dependence.Comment: 17 pages, 12 figures, accepted at Phys. Rev. E. v4 is almost identical to the final paper version. It includes, compared to former versions v2/v3, no new physical content, but only some corrected formulas in the appendices and corrected typos in text. In comparison to version v1, in v2-v4 some new results have been included and text has been change

The Magic of Permutation Matrices: Categorizing, Counting and Eigenspectra of Magic Squares

Permutation matrices play an important role in understand the structure of magic squares. In this work, we use a class of symmetric permutation matrices than can be used to categorize magic squares. Many magic squares with a high degree of symmetry are studied, including classes that are generalizations of those categorized by Dudeney in 1917. We show that two classes of such magic squares are singular and the eigenspectra of such magic squares are highly structured. Lastly, we prove that natural magic squares of singly-even order of these classes do note exist.Comment: 26 page