90 research outputs found
Robust skyrmion-bubble textures in SrRuO thin films stabilized by magnetic anisotropy
Topological spin textures in an itinerant ferromagnet, SrRuO is studied
combining Hall transport measurements and numerical simulations. We observe
characteristic signatures of the Topological Hall Effect associated with
skyrmions. A relatively large thickness of our films and absence of heavy metal
layers make the interfacial Dzyaloshinskii-Moriya interaction an unlikely
source of these topological spin textures. Additionally, the transport
anomalies exhibit an unprecedented robustness to magnetic field tilting and
temperature. Our numerical simulations suggest that this unconventional
behavior results from magnetic bubbles with skyrmion topology stabilized by
magnetodipolar interactions in an unexpected region of parameter space.Comment: 6 pages, 7 figure
Effects of crack tip geometry on dislocation emission and cleavage: A possible path to enhanced ductility
We present a systematic study of the effect of crack blunting on subsequent
crack propagation and dislocation emission. We show that the stress intensity
factor required to propagate the crack is increased as the crack is blunted by
up to thirteen atomic layers, but only by a relatively modest amount for a
crack with a sharp 60 corner. The effect of the blunting is far less
than would be expected from a smoothly blunted crack; the sharp corners
preserve the stress concentration, reducing the effect of the blunting.
However, for some material parameters blunting changes the preferred
deformation mode from brittle cleavage to dislocation emission. In such
materials, the absorption of preexisting dislocations by the crack tip can
cause the crack tip to be locally arrested, causing a significant increase in
the microscopic toughness of the crack tip. Continuum plasticity models have
shown that even a moderate increase in the microscopic toughness can lead to an
increase in the macroscopic fracture toughness of the material by several
orders of magnitude. We thus propose an atomic-scale mechanism at the crack
tip, that ultimately may lead to a high fracture toughness in some materials
where a sharp crack would seem to be able to propagate in a brittle manner.
Results for blunt cracks loaded in mode II are also presented.Comment: 12 pages, REVTeX using epsfig.sty. 13 PostScript figures. Final
version to appear in Phys. Rev. B. Main changes: Discussion slightly
shortened, one figure remove
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Argonne National Laboratory Reports
The behavior of FTR-type, mixed-oxide, pre-irradiated "high-power-structure" fuel during a simulation of an FTR loss-of-flow accident was studied in the Mark-IIA integral TREAT loop. Analysis of the data leads to a postulated scenario (sequence and timing) of events in this test. This scenario is presented, together with the calculated timing of events obtained by use of SAS code
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Above cutoff impedance measurements of pumping holes for the collider liner
A holed liner was considered for the Superconducting Super Collider (SSC) Collider Ring because of vacuum problems caused by photon-induced desorption. The liner would serve to shield the cold surface of the beam tube from the synchrotron radiation and the holes (or slots) would allow distributed pumping by gas-absorption material that could be placed between the liner and the beam tube. The impedance of holes and slots in a liner were studied by means of simulations using both MAFIA and HFSS, analytical modelling, wire measurements and electron beam measurements
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Argonne National Laboratory Reports
The behavior of FTR-type, mixed-oxide, pre-irradiated, ''intermediate-power-structure'' fuel during a simulation of an FTR loss-of-flow accident was studied in the Mark-IIA integral TREAT loop. Analysis of the data reported here leads to a postulated scenario (sequence and timing) of events in the test. This scenario is presented, together with the calculated timing of events obtained by use of the SAS code
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Summary and evaluation: fuel dynamics loss-of-flow experiments (tests L2, L3, and L4)
Three similar experiments conducted to support the analyses of hypothetical LMFBR unprotected-loss-of-flow accidents are summarized and evaluated. The tests, designated L2, L3, and L4, provided experimental data against which accident-analysis codes could be compared, so as to guide further analysis and modeling of the initiating phases of the hypothetical accident. The tests were conducted using seven-pin bundles of mixed-oxide fuel pins in Mark-II flowing-sodium loops in the TREAT reactor. Test L2 used fresh fuel. Tests L3 and L4 used irradiated fuel pins having, respectively, ''intermediate-power'' (no central void) and ''high-power'' (fully developed central void) microstructure. 12 references. (auth
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