167,832 research outputs found
Structure and thermal cycling stability of a hafnium monocarbide reinforced directionally solidified cobalt-base eutectic alloy
A nominal composition of Co-15Cr-2ONi-10.5 Hf-0.7 C (NASA-HAFCO-11) was directionally solidified at 0.8 cm/hr growth rate to produce aligned HfC in a cobalt matrix alloy. The aligned HfC fibers were present as rod and plate types. The diameter of the aligned fibers was about 1 micron, with volume fraction in the range of 11 to 15 percent. The growth direction of the fibers was parallel to the 100. The NASA-HAFCO-11 alloy was subjected to thermal cycling between 425 deg and 1100 C, using a 2.5 minute cycle. No microstructural degradation of the HfC fibers in the alloy was observed after 2500 cycles
Dominant mobility modulation by the electric field effect at the LaAlO_3 / SrTiO_3 interface
Caviglia et al. [Nature (London) 456, 624 (2008)] have found that the
superconducting LaAlO_3 / SrTiO_3 interface can be gate modulated. A central
issue is to determine the principal effect of the applied electric field. Using
magnetotransport studies of a gated structure, we find that the mobility
variation is almost five times as large as the sheet carrier density.
Furthermore, superconductivity can be suppressed at both positive and negative
gate bias. These results indicate that the relative disorder strength strongly
increases across the superconductor-insulator transition.Comment: 4 pages, 4 figure
The effects of surface finish and grain size on the strength of sintered silicon carbide
The effects of surface treatment and microstructure, especially abnormal grain growth, on the strength of sintered SiC were studied. The surfaces of sintered SiC were treated with 400, 800 and 1200 grit diamond wheels. Grain growth was induced by increasing the sintering times at 2050 C. The beta to alpha transformation occurred during the sintering of beta-phase starting materials and was often accompanied by abnormal grain growth. The overall strength distributions were established using Weibull statistics. The strength of the sintered SiC is limited by extrinsic surface flaws in normal-sintered specimens. The finer the surface finish and grain size, the higher the strength. But the strength of abnormal sintering specimens is limited by the abnormally grown large tabular grains. The Weibull modulus increases with decreasing grain size and decreasing grit size for grinding
Anisotropic Dirac fermions in a Bi square net of SrMnBi2
We report the highly anisotropic Dirac fermions in a Bi square net of
SrMnBi2, based on a first principle calculation, angle resolved photoemission
spectroscopy, and quantum oscillations for high-quality single crystals. We
found that the Dirac dispersion is generally induced in the (SrBi)+ layer
containing a double-sized Bi square net. In contrast to the commonly observed
isotropic Dirac cone, the Dirac cone in SrMnBi2 is highly anisotropic with a
large momentum-dependent disparity of Fermi velocities of ~ 8. These findings
demonstrate that a Bi square net, a common building block of various layered
pnictides, provide a new platform that hosts highly anisotropic Dirac fermions.Comment: 5 pages, 4 figure
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