4,204 research outputs found
Directionally solidified iron-base eutectic alloys
Pseudobinary eutectic alloys with nominal compositions of Fe-25Ta-22Ni-10Cr and Fe-15.5Nb-14.5Ni-6.0Cr were directionally solidified at 0.5 centimeter per hour. Their microstructure consisted of the fcc, iron solid-solution, matrix phase reinforced by about 41-volume-percent, hcp, faceted Fe2Ta fibers and 41-volume-percent, hcp, Fe2Nb lamellae for the tantalum- and niobium-containing alloys, respectively. The microstructural stability under thermal cycling and the temperature dependence of tensile properties were investigated. These alloys showed low elevated-temperature strength and were not considered suitable for application in aircraft-gas-turbine blades although they may have applicability as vane materials
Directionally solidified eutectic alloy gamma-beta
A pseudobinary eutectic alloy composition was determined by a previously developed bleed-out technique. The directionally solidified eutectic alloy with a composition of Ni-37.4Fe-10.0Cr-9.6Al (in wt%) had tensile strengths decreasing from 1,090 MPa at room temperature to 54 MPa at 1,100 C. The low density, excellent microstructural stability, and oxidation resistance of the alloy during thermal cycling suggest that it might have applicability as a gas turbine vane alloy while its relatively low high temperature strength precludes its use as a blade alloy. A zirconium addition increased the 750 C strength, and a tungsten addition was ineffective. The gamma=beta eutectic alloys appeared to obey a normal freezing relation
Angle-resolved photoemission spectra in the cuprates from the d-density wave theory
Angle-resolved photoemission spectra present two challenges for the d-density
wave (DDW) theory of the pseudogap state of the cuprates: (1) hole pockets near
are not observed, in apparent contradiction with the assumption
of translational symmetry breaking, and (2) there are no well-defined
quasiparticles at the {\it antinodal} points, in contradiction with the
predictions of mean-field theory of this broken symmetry state. Here, we show
how these puzzles can be resolved.Comment: 4 pages, 3 eps figures, RevTex
Berry phase theory of planar Hall effect in Topological Insulators
Negative longitudinal magnetoresistance, in the presence of an external
magnetic field parallel to the direction of an applied current, has recently
been experimentally verified in Weyl semimetals and topological insulators in
the bulk conduction limit. The appearance of negative longitudinal
magnetoresistance in topological semimetals is understood as an effect of
chiral anomaly, whereas it is not well-defined in topological insulators.
Another intriguing phenomenon, planar Hall effect - appearance of a transverse
voltage in the plane of applied co-planar electric and magnetic fields not
perfectly aligned to each other, a configuration in which the conventional Hall
effect vanishes, has recently been suggested to exist in Weyl semimetals. In
this paper we present a quasi-classical theory of planar Hall effect of a
three-dimensional topological insulator in the bulk conduction limit. Starting
from Boltzmann transport equations we derive the expressions for planar Hall
conductivity and longitudinal magnetoconductivity in topological insulators and
show the important roles played by the orbital magnetic moment for the
appearance of planar Hall effect. Our theoretical results predict specific
experimental signatures for topological insulators that can be directly checked
in experiments.Comment: 18 pages, 3 figure
Macrosegregation during plane front directional solidification of Csl-1 wt. percent Tll alloy
Macrosegregation produced during vertical Bridgeman directional solidification of Csl-1 wt. pct. Tll in crucibles of varying diameter, from 0.5 to 2.0 cm, was examined. Gravity driven convection is present in the melt even in the smallest crucible diameter of 0.5 cm. Observed solutal profiles are in agreement with the analytical boundary layer model of Favier which describes macrosegregation in the presence of convection. The scintillation efficiency of Csl decreases along the specimen length as the thallium iodide content of the alloy increases
Bell's inequality and universal quantum gates in a cold atom chiral fermionic p-wave superfluid
We propose and analyze a probabilistic scheme to entangle two spatially
separated topological qubits in a superfluid using controlled
collisions between atoms in movable dipole traps and unpaired atoms inside
vortex cores in the superfluid. We discuss how to test the violation of Bell's
inequality with the generated entanglement. A set of universal quantum gates is
shown to be implementable \textit{deterministically} using the entanglement
despite the fact that the entangled states can only be created
probabilistically.Comment: 4+ pages, 3 figures, display problems of figures in previous version
are corrected, accepted for publication in PR
Primary arm spacing in chill block melt spun Ni-Mo alloys
Chill block melt spun ribbons of Ni-Mo binary alloys containing 8.0 to 41.8 wt % Mo have been prepared under carefully controlled processing conditions. The growth velocity has been determined as a function of distance from the quench surface from the observed ribbon thickness dependence on the melt puddle residence time. Primary arm spacings measured at the midribbon thickness locations show a dependence on growth velocity and alloy composition which is expected from dendritic growth models for binary alloys directionally solidified in a positive temperature gradient
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