54 research outputs found
Phonon-mediated anisotropic superconductivity in the Y and Lu nickel borocarbides
We present scanning tunneling spectroscopy and microscopy measurements at low
temperatures in the borocarbide materials RNi2B2C (R=Y, Lu). The characteristic
strong coupling structure due to the pairing interaction is unambiguously
resolved in the superconducting density of states. It is located at the
superconducting gap plus the energy corresponding to a phonon mode identified
in previous neutron scattering experiments. These measurements also show that
this mode is coupled to the electrons through a highly anisotropic
electron-phonon interaction originated by a nesting feature of the Fermi
surface. Our experiments, from which we can extract a large electron-phonon
coupling parameter lambda (between 0.5 and 0.8), demonstrate that this
anisotropic electron-phonon coupling has an essential contribution to the
pairing interaction. The tunneling spectra show an anisotropic s-wave
superconducting gap function.Comment: 5 pages, 3 figure
Pulsar-wind nebulae and magnetar outflows: observations at radio, X-ray, and gamma-ray wavelengths
We review observations of several classes of neutron-star-powered outflows:
pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe
interacting directly with interstellar medium (ISM), and magnetar-powered
outflows. We describe radio, X-ray, and gamma-ray observations of PWNe,
focusing first on integrated spectral-energy distributions (SEDs) and global
spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering
array of morphologies, with jets, trails, and other structures. Several of the
23 so far identified magnetars show evidence for continuous or sporadic
emission of material, sometimes associated with giant flares, and a few
possible "magnetar-wind nebulae" have been recently identified.Comment: 61 pages, 44 figures (reduced in quality for size reasons). Published
in Space Science Reviews, "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray
Bursts and Blazars: Physics of Extreme Energy Release
Reading, metacognition, and motivation: A follow-up study of German students in Grades 7 and 8
This follow-up study to van Kraayenoord and Schneider (1999) examined the performance in reading, metacognition and motivation related to reading of students in Grades 7 and 8. Results showed significant correlations between all of the variables. A multivariate analysis of variance showed that good and poor readers differed in reading self-concept and metacognitive measures related to reading and memory. A stepwise regression analysis suggested that the metacognitive variables were the best predictors of reading. Furthermore, a comparison of the results of the previous study with those of the current investigation revealed that the findings were stable over time. Since the period between the two studies is the time during which students make important decisions related to enrolment in one of three distinct school-types in Germany, we examined the results of various groups of students: those in Gymnasium (high educational track), Realschule (middle educational track), and Hauptschule (low educational track). Students in the Gymnasium scored significantly better than students in the other two groups on almost all variables related to reading. A re-analysis of the data from our first investigation found that the results of the Gymnasium students in the second study could be predicted from their results obtained during elementary school
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