2,864 research outputs found
New results on heavy hadron spectroscopy with NRQCD
We present results for the spectrum of b-bbar bound states in the quenched
approximation for three different values of the lattice spacing. Results for
spin-independent splittings are shown to have good scaling behaviour;
spin-dependent splittings are more sensitive to discretisation effects. We
discuss what needs to be done to match the experimental spectrum.Comment: 3 pages, contribution to Lattice'9
A small sealed Ta crucible for thermal analysis of volatile metallic samples
Differential thermal analysis on metallic alloys containing volatile elements
can be highly problematic. Here we show how measurements can be performed in
commercial, small-sample, equipment without modification. This is achieved by
using a sealed Ta crucible, easily fabricated from Ta tubing and sealed in a
standard arc furnace. The crucible performance is demonstrated by measurements
on a mixture of Mg and MgB, after heating up to 1470. We
also show data, measured on an alloy with composition GdMg, that
clearly shows both the liquidus and a peritectic, and is consistent with
published phase diagram data
Probing fractal magnetic domains on multiple length scales in Nd2Fe14B
Using small-angle neutron scattering, we demonstrate that the complex
magnetic domain patterns at the surface of Nd2Fe14B, revealed by quantitative
Kerr and Faraday microscopy, propagate into the bulk and exhibit structural
features with dimensions down to 6 nm, the domain wall thickness. The observed
fractal nature of the domain structures provides an explanation for the
anomalous increase in the bulk magnetization of Nd2Fe14B below the
spin-reorientation transition. These measurements open up a rich playground for
studies of fractal structures in highly anisotropic magnetic systems.Comment: Accepted for publication in Phys. Rev. Lett. (4 pages, 4 figures
Low temperature heat capacity of Fe_{1-x}Ga_{x} alloys with large magneostriction
The low temperature heat capacity C_{p} of Fe_{1-x}Ga_{x} alloys with large
magnetostriction has been investigated. The data were analyzed in the standard
way using electron () and phonon () contributions. The
Debye temperature decreases approximately linearly with increasing
Ga concentration, consistent with previous resonant ultrasound measurements and
measured phonon dispersion curves. Calculations of from lattice
dynamical models and from measured elastic constants C_{11}, C_{12} and C_{44}
are in agreement with the measured data. The linear coefficient of electronic
specific heat remains relatively constant as the Ga concentration
increases, despite the fact that the magnetoelastic coupling increases. Band
structure calculations show that this is due to the compensation of majority
and minority spin states at the Fermi level.Comment: 14 pages, 6 figure
Phase transitions and iron-ordered moment form factor in LaFeAsO
Elastic neutron scattering studies of an optimized LaFeAsO single crystal
reveal that upon cooling, an onset of the tetragonal (T)-to-orthorhombic (O)
structural transition occurs at K, and it exhibits a
sharp transition at K. We argue that in the
temperature range to , T and O structures may
dynamically coexist possibly due to nematic spin correlations recently proposed
for the iron pnictides, and we attribute to the formation of
long-range O domains from the finite local precursors. The antiferromagnetic
structure emerges at K, with the iron moment
direction along the O \emph{a} axis. We extract the iron magnetic form factor
and use the tabulated of Fe, Fe and Fe to
obtain a magnetic moment size of 0.8 at 9.5 K.Comment: 7 pages, 6 figures, 3 table
Virtual Teaching Together: Engaging Parents and Young Children in STEM Activities
INTRODUCTION: Early informal learning experiences are essential for sparking long-term interest in science, technology, engineering, and math (STEM). In a prior study, we found more promising parent involvement outcomes when families of young children were provided with STEM family education events along with home STEM activity kits compared to providing workshops alone. This study was a conceptual replication using the same program-
METHODS: Museum informal science educators introduced four units via virtual video chat sessions linked to 12 hands-on STEM activities that were mailed to families randomly assigned to the treatment group. Half of the families were assigned to a waitlist control group that received a portion of the virtual program after the posttest. Participants included 60 families with children aged 3 to 5 years from diverse linguistic and socioeconomic backgrounds.
RESULTS: Our results indicate no significant group differences in the primary outcome of parents\u27 involvement in informal STEM but a small, positive effect size (ES = 0.18) that was similar in magnitude to the prior, in-person study. Although parents mostly perceived the remote delivery as convenient and the materials as engaging for their child, there were no significant program impacts on children\u27s general science interests (ES = -0.19).
DISCUSSION: Despite the convenience, parents reported time was a barrier to doing STEM activities at home. Parents with lower education levels were less likely to attend, suggesting virtual approaches are not sufficient for ensuring broad access to family engagement programs for populations underrepresented in STEM
Discovery of a binary icosahedral quasicrystal in ScZn
We report the discovery of a new binary icosahedral phase in a Sc-Zn alloy
obtained through solution-growth, producing millimeter-sized, facetted, single
grain, quasicrystals that exhibit different growth morphologies, pentagonal
dodecahedra and rhombic triacontahedra, under only marginally different growth
conditions. These two morphologies manifest different degrees of
quasicrystalline order, or phason strain. The discovery of i-ScZn
suggests that a reexamination of binary phase diagrams at compositions close to
crystalline approximant structures may reveal other, new binary
quasicrystalline phases.Comment: Incorrect spelling in author list resolve
The static quark-antiquark potential in QCD to three loops
The static potential between an infinitely heavy quark and antiquark is
derived in the framework of perturbative QCD to three loops by performing a
full calculation of the two-loop diagrams and using the renormalization group.
The contribution of massless fermions is included.Comment: Latex, 11 pages, 3 figures included. The complete paper, including
figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/ . Revised version,
essentially identical to the version published in Physical Review Letter
- …