3,364 research outputs found
Wireless Keypads - A New Classroom Technology Using Enhanced Multiple-Choice Questions
This article discusses the advantages of using wireless keypads in the
Lecture/classroom. This new technology requires multiple-choice (MC) questions
to mate with the keypad entry features of these devices. The format of the
traditional MC response is constrained to five choices and only one best
response is allowed. For this reason, we propose enhancements to the
traditional MC question. This enhanced MC question allows as many as ten
answers. The answers can vary in their degree of correctness and can be
assigned partial credit. By combining wireless keypads and multiple-choice
questions, we can readily perform both formative and summative assessments of
student learning. Examples and classroom applications are presented.Comment: pdf file, 8 pages,
Teaching "Symmetry" in the Introductory Physics Curriculum
Modern physics is largely defined by fundamental symmetry principles and
Noether's Theorem. Yet these are not taught, or rarely mentioned, to beginning
students, thus missing an opportunity to reveal that the subject of physics is
as lively and contemporary as molecular biology, and as beautiful as the arts.
We prescribe a symmetry module to insert into the curriculum, of a week's
length.Comment: 15 pages, 4 figure
Magnetoelectric properties of 500 nm Cr2O3 films
The linear magnetoelectric effect was measured in 500 nm Cr2O3 films grown by
rf sputtering on Al2O3 substrates between top and bottom thin film Pt
electrodes. Magnetoelectric susceptibility was measured directly by applying an
AC electric field and measuring the induced AC magnetic moment using
superconducting quantum interference device magnetometry. A linear dependence
of the induced AC magnetic moment on the AC electric field amplitude was found.
The temperature dependence of the magnetoelectric susceptibility agreed
qualitatively and quantitatively with prior measurements of bulk single
crystals, but the characteristic temperatures of the film were lower than those
of single crystals. It was also possible to reverse the sign of the
magnetoelectric susceptibility by reversing the sign of the magnetic field
applied during cooling through the N\'eel temperature. A competition between
total magnetoelectric and Zeeman energies is proposed to explain the difference
between film and bulk Cr2O3 regarding the cooling field dependence of the
magnetoelectric effect.Comment: accepted at Physical Review
Safety First! : March and Two - Step
https://digitalcommons.library.umaine.edu/mmb-ps/2946/thumbnail.jp
Effects of hydrogen/deuterium absorption on the magnetic properties of Co/Pd multilayers
The effects of hydrogen (H2) and deuterium (D2) absorption were studied in
two Co/Pd multilayers with perpendicular magnetic anisotropy (PMA) using
polarized neutron reflectivity (PNR). PNR was measured in an external magnetic
field H applied in the plane of the sample with the magnetization M confined in
the plane for {\mu}_o H= 6.0 T and partially out of plane at 0.65 T. Nominal
thicknesses of the Co and Pd layers were 2.5 {\AA} and 21 {\AA}, respectively.
Because of these small values, the actual layer chemical composition,
thickness, and interface roughness parameters were determined from the nuclear
scattering length density profile ({\rho}_n) and its derivative obtained from
both x-ray reflectivity and PNR, and uncertainties were determined using Monte
Carlo analysis. The PNR {\rho}_n showed that although D2 absorption occurred
throughout the samples, absorption in the multilayer stack was modest (0.02 D
per Pd atom) and thus did not expand. Direct magnetometry showed that H2
absorption decreased the total M at saturation and increased the component of M
in the plane of the sample when not at saturation. The PNR magnetic scattering
length density ({\rho}_m) revealed that the Pd layers in the multilayer stack
were magnetized and that their magnetization was preferentially modified upon
D2 absorption. In one sample, a modulation of M with twice the multilayer
period was observed at {\mu}_o H= 0.65 T, which increased upon D2 absorption.
These results indicate that H2 or D2 absorption decreases both the PMA and
total magnetization of the samples. The lack of measurable expansion during
absorption indicates that these changes are primarily governed by modification
of the electronic structure of the material.Comment: to appear in Physics review B, 201
Magnetization Switching in Single-Domain Ferromagnets
A model for single-domain uniaxial ferromagnetic particles with high
anisotropy, the Ising model, is studied. Recent experimental observations have
been made of the probability that the magnetization has not switched. Here an
approach is described in which it is emphasized that a ferromagnetic particle
in an unfavorable field is in fact a metastable system, and the switching is
accomplished through the nucleation and subsequent growth of localized
droplets. Nucleation theory is applied to finite systems to determine the
coercivity as a function of particle size and to calculate the probability of
not switching. Both of these quantities are modified by different boundary
conditions, magnetostatic interactions, and quenched disorder.Comment: 4 pages, LaTeX, 2 figures, documentstyle{elsart} More fits and
Mathematica notebook at http://www.scri.fsu.edu/~novotny/magnetism.html To
appear in J.Mag.Mag.Mater. Conference Proceedings of 7th International
Conference on Magnetism Cairns, Australia, August, 199
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